U.S. patent application number 13/759970 was filed with the patent office on 2013-06-13 for extreme ultraviolet light source device, laser light source device for extreme ultraviolet light source device, and method of adjusting laser light source device for extreme ultraviolet light source device.
This patent application is currently assigned to GIGAPHOTON INC.. The applicant listed for this patent is Gigaphoton Inc.. Invention is credited to Hideo HOSHINO, Hakaru MIZOGUCHI, Masato MORIYA, Osamu WAKABAYASHI.
Application Number | 20130148677 13/759970 |
Document ID | / |
Family ID | 42055227 |
Filed Date | 2013-06-13 |
United States Patent
Application |
20130148677 |
Kind Code |
A1 |
MORIYA; Masato ; et
al. |
June 13, 2013 |
EXTREME ULTRAVIOLET LIGHT SOURCE DEVICE, LASER LIGHT SOURCE DEVICE
FOR EXTREME ULTRAVIOLET LIGHT SOURCE DEVICE, AND METHOD OF
ADJUSTING LASER LIGHT SOURCE DEVICE FOR EXTREME ULTRAVIOLET LIGHT
SOURCE DEVICE
Abstract
An EUV light source device properly compensates the wave front
of laser beam which is changed by heat. A wave front compensator
and a sensor are provided in an amplification system which
amplifies laser beam. The sensor detects and outputs changes in the
angle (direction) of laser beam and the curvature of the wave front
thereof. A wave front compensation controller outputs a signal to
the wave front compensator based on the measurement results from
the sensor. The wave front compensator corrects the wave front of
the laser beam to a predetermined wave front according to an
instruction from the wave front compensation controller.
Inventors: |
MORIYA; Masato;
(Hiratsuka-shi, JP) ; HOSHINO; Hideo;
(Hiratsuka-shi, JP) ; WAKABAYASHI; Osamu;
(Hiratsuka-shi, JP) ; MIZOGUCHI; Hakaru;
(Hiratsuka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gigaphoton Inc.; |
Oyama-shi |
|
JP |
|
|
Assignee: |
GIGAPHOTON INC.
Oyama-shi
JP
|
Family ID: |
42055227 |
Appl. No.: |
13/759970 |
Filed: |
February 5, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12560864 |
Sep 16, 2009 |
8395133 |
|
|
13759970 |
|
|
|
|
Current U.S.
Class: |
372/29.014 |
Current CPC
Class: |
H01S 3/1061 20130101;
H01S 3/2316 20130101; H01S 3/0064 20130101; H05G 2/003 20130101;
H01S 3/034 20130101; H01S 3/10 20130101; H01S 3/1307 20130101; H01S
3/2232 20130101; H05G 2/008 20130101; H01S 3/136 20130101; H01S
3/005 20130101; H05G 2/005 20130101 |
Class at
Publication: |
372/29.014 |
International
Class: |
H01S 3/10 20060101
H01S003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 19, 2008 |
JP |
2008-240915 |
Jan 16, 2009 |
JP |
2009-008001 |
Sep 14, 2009 |
JP |
2009-212003 |
Claims
1.-13. (canceled)
14. A laser light source device for use in an extreme ultraviolet
light source device, comprising: a laser oscillator that outputs
laser beam; an amplification system that amplifies the laser beam
output from the laser oscillator by at least one amplifier; and a
focusing system that inputs the laser beam, amplified by the
amplification system, into a chamber of the extreme ultraviolet
light source device, at least the amplification system being
provided with at least one first compensation unit that compensates
a direction of laser beam and a shape of a wave front thereof in
the amplification system to a predetermined direction and a
predetermined wave front shape, and at least one compensation
control unit that controls a compensation operation by the first
compensation unit.
15.-21. (canceled)
22. A laser light source device comprising: a laser oscillator that
outputs laser beam; an amplification system that amplifies the
laser beam output from the laser oscillator by at least one
amplifier; and a focusing system that inputs the laser beam,
amplified by the amplification system, into a chamber of the
extreme ultraviolet light source device, at least the amplification
system being provided with at least one first compensation unit
that compensates a direction of laser beam and a shape of a wave
front thereof in the amplification system to a predetermined
direction and a predetermined wave front shape, and at least one
compensation control unit that controls a compensation operation by
the first compensation unit.
23. The laser light source device according to claim 22, wherein a
diamond window is used as a window of the chamber, or a window of
the amplifier.
24.-28. (canceled)
29. The laser light source device according to claim 22, wherein a
plurality of first compensation units s are provided in the
amplification system, and the compensation control unit controls
the compensation operations of the first compensation units in
order from one located upstream in a traveling direction of the
laser beam to compensate the direction of the laser beam and the
shape of the wave front thereof to the predetermined direction and
the predetermined wave front shape.
30. A laser light source device comprising: a laser oscillator that
outputs laser beam; an amplification system that amplifies the
laser beam output from the laser oscillator by at least one
amplifier; and a focusing system that inputs the laser beam,
amplified by the amplification system, into a chamber of the
extreme ultraviolet light source device, at least the amplification
system being provided with at least one first compensation unit
that compensates a direction of laser beam in the amplification
system to a predetermined direction, at least one compensation
control unit that controls a compensation operation by the first
compensation unit.
31. The laser light source device according to claim 30, wherein a
plurality of first compensation units are provided in the
amplification system, and the compensation control unit controls
the compensation operations of the first compensation units in
order from one located upstream in a traveling direction of the
laser beam to compensate the direction of the laser beam to the
predetermined direction.
32.-34. (canceled)
35. The laser light source device according to claim 22, wherein a
mirror for inputting the laser beam to the first compensation unit
is provided with a cooling mechanism for cooling a mirror surface
in an axial symmetrical fashion.
36. (canceled)
37. The laser light source device according to claim 30, wherein a
minor for inputting the laser beam to the first compensation unit
is provided with a cooling mechanism for cooling a mirror surface
in an axial symmetrical fashion.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an extreme ultraviolet
light source device, a laser light source device for an extreme
ultraviolet light source device, and a method of adjusting a laser
light source device for an extreme ultraviolet light source
device.
[0002] A semiconductor chip is created, for example, by reduction
projection of a mask on which a circuit pattern is drawn onto a
wafer having a resist applied thereon, and by repeatedly performing
processing, such as etching and of thin film formation. The
progressive reduction of the scale of semiconductor processing
demands the use of radiation of further short wavelength.
[0003] Accordingly, research has been made on a semiconductor
exposure technique which uses radiation of extremely short
wavelength of 13.5 nm or so and a reduction optics system. This
type of technique is termed EUVL (Extreme Ultra Violet Lithography:
exposure using extreme ultraviolet light). Hereinafter, extreme
ultraviolet light will be abbreviated as "EUV light".
[0004] Three types of EUV light sources are known: an LPP (Laser
Produced Plasma: plasma produced by a laser) type light source, a
DPP (Discharge Produced Plasma) type light source, and an SR
(Synchrotron Radiation) type light source.
[0005] The LPP type light source is a light source which generates
a plasma by irradiating laser beam on a target material, and
employs EUV radiation emitted from this plasma. The DPP type light
source is a light source which employs a plasma generated by an
electrical discharge. The SR (synchrotron radiation) is a light
source which uses orbital radiation. Of those three types of light
sources, the LPP type light source is more likely to acquire
high-output EUV radiation as compared to the other two types
because the LPP type light source can provide an increased plasma
density, and can ensure a larger solid angle over which the
radiation is collected.
[0006] To acquire high-power laser beam at a high repeating
frequency, therefore, a laser light source device configured
according to the MOPA (Master Oscillator Power Amplifier) system is
proposed (JP-A-2006-128157).
[0007] An art of regulating the wave front of laser beam using a
deformable mirror whose surface shape can be variable controlled
freely to some extent is known (JP-A-2003-270551).
[0008] To acquire EUV radiation of 100 W to 200 W or so, for
example, it is necessary to set the output of a carbon dioxide gas
laser as driver laser beam to 10 to 20 kW or so. The use of such
high-power laser beam causes various optical elements in the
optical path to absorb radiation and thus become hot, so that the
shape and direction of the wave front of laser beam change. It is
described herein that the wave front of laser beam includes the
shape and direction of the wave front of laser beam.
[0009] When high-power laser beam passes through a lens or a
window, the shape and refractive index of the lens or window vary
due to a heat-originated temperature increase, changing the wave
front of laser beam. When the wave front of laser beam changes, for
example, the laser beam cannot be efficiently input to an
amplification area in a laser amplifier, so that a laser output
cannot be acquired as expected. Further, because the focal position
of laser beam which is input into the chamber changes according to
a change in the wave front of the laser beam, the laser beam cannot
be efficiently irradiated on a target material, thus lowering the
power of the EUV radiation.
SUMMARY OF THE INVENTION
[0010] Accordingly, the present invention addresses the
above-identified problems, and it is an object of the invention to
provide an extreme ultraviolet light source device, a laser light
source device for an extreme ultraviolet light source device, and a
method of adjusting a laser light source device for an extreme
ultraviolet light source device, which can compensate the direction
of laser beam and the shape of the wave front thereof to a
predetermined direction and predetermined wave front shape. It is
another object of the invention to provide an extreme ultraviolet
light source device, a laser light source device for an extreme
ultraviolet light source device, and a method of adjusting a laser
light source device for an extreme ultraviolet light source device,
which can compensate the direction of laser beam and the shape of
the wave front thereof at a plurality of locations set on an
optical path, and perform control in such a way that the
compensation operations at the individual locations do not cause
contention. Further objects of the invention may be readily
apparent from the following description of the presently preferred
embodiments.
[0011] To achieve the objects, according to a first aspect of the
invention, there is provided an extreme ultraviolet light source
device that generates extreme ultraviolet by irradiating laser beam
on a target material for turning the target material into plasma,
comprising a target material supply unit that supplies the target
material into a chamber, a laser oscillator that outputs laser
beam, an amplification system that amplifies the laser beam output
from the laser oscillator by at least one amplifier, and a focusing
system for irradiating the laser beam, amplified by the
amplification system, on the target material in the chamber.
Further, at least the amplification system is provided with at
least one first detection unit that detects a direction of laser
beam and a shape of a wave front thereof in the amplification
system, or detects beam parameters equivalent to the direction of
the laser beam and the shape of the wave front thereof in the
amplification system, at least one first compensation unit that
compensates the direction of the laser beam and the shape of the
wave front thereof which are detected by the first detection unit
to a predetermined direction and a predetermined wave front shape,
and at least one compensation control unit that controls a
compensation operation by the first compensation unit according to
a result of detection performed by the first detection unit.
[0012] The focusing system can be provided with at least one second
compensation unit separate from the first compensation unit, and at
least one second detection unit separate from the first detection
unit.
[0013] When a plurality of first compensation units are provided in
the amplification system, the compensation control unit controls
the compensation operations of the first compensation units
according to a predetermined sequence set beforehand to compensate
the direction of the laser beam and the shape of the wave front
thereof to the predetermined direction and the predetermined wave
front shape. For example, the compensation control unit controls
the compensation operations of the first compensation units in
order from one located upstream in a traveling direction of the
laser beam.
[0014] The compensation control unit can control the compensation
operation of the first compensation unit and a compensation
operation of the second compensation unit according to a
predetermined sequence set beforehand to compensate the direction
of the laser beam and the shape of the wave front thereof to the
predetermined direction and the predetermined wave front shape. For
example, the compensation control unit can control the compensation
operation of the second compensation unit after controlling the
compensation operation of the first compensation unit.
[0015] The at least one amplifier is classified into a preamplifier
provided upstream in a traveling direction of the laser beam and a
main amplifier provided downstream in the traveling direction of
the laser beam, and the first compensation unit is provided
upstream or downstream of at least the preamplifier.
[0016] The target material supply unit can supply the target
material into the chamber after the first compensation unit
compensates the direction of the laser beam and the shape of the
wave front thereof to the predetermined direction and the
predetermined wave front shape. Alternatively, the target material
supply unit can supply the target material into the chamber after
the first compensation unit and the second compensation unit
respectively compensate the direction of the laser beam and the
shape of the wave front thereof to the predetermined direction and
the predetermined wave front shape.
[0017] The amplification system can be provided with a saturable
absorber for absorbing laser beam of a predetermined value or
less.
[0018] The first compensation unit may have an angle compensation
capability for adjusting an outgoing angle of the laser beam in the
predetermined direction, and a curvature compensation capability
for adjusting a curvature of the wave front of the laser beam to
the predetermined wave front shape.
[0019] The first compensation unit can be configured as a
reflection optical system including a mirror capable of variably
controlling a curvature.
[0020] The first detection unit can be configured to include a
reflection mirror that reflects the laser beam, and an optical
sensor that detects a state of leak radiation transmitting through
the reflection mirror as an electric signal.
[0021] According to a second aspect of the invention, there is
provided a laser light source device for use in an extreme
ultraviolet light source device, comprising a laser oscillator that
outputs laser beam, an amplification system that amplifies the
laser beam output from the laser oscillator by at least one
amplifier, and a focusing system that inputs the laser beam,
amplified by the amplification system, into a chamber of the
extreme ultraviolet light source device. Further, at least the
amplification system is provided with at least one first
compensation unit that compensates a direction of laser beam and a
shape of a wave front thereof in the amplification system to a
predetermined direction and a predetermined wave front shape, and
at least one compensation control unit that controls a compensation
operation by the first compensation unit.
[0022] According to a third aspect of the invention, there is
provided a method of adjusting a laser light source device for use
in an extreme ultraviolet light source device, the laser light
source device including a an amplification system that amplifies
laser beam output from a laser oscillator by at least one
amplifier, and a focusing system that inputs the laser beam,
amplified by the amplification system, into a chamber of the
extreme ultraviolet light source device, the method comprising
outputting the laser beam from the laser oscillator, detecting a
direction of the laser beam amplified by the amplifier and a shape
of a wave front thereof, and compensating the detected direction of
the laser beam and the detected shape of the wave front thereof to
a predetermined direction and a predetermined wave front shape.
[0023] A Shack-Hartmann wave front instrument may be included as a
detector that detects the direction of the laser beam and the shape
of the wave front thereof.
[0024] A beam pointing measuring instrument and a beam profile
measuring instrument may be included as a detector that detects the
beam parameters equivalent to the direction of the laser beam and
the shape of the wave front thereof.
[0025] At least two beam profile measuring instruments may be
included as a detector that detects the beam parameters equivalent
to the direction of the laser beam and the shape of the wave front
thereof.
[0026] The extreme ultraviolet light source device according to the
first aspect may be configured in such a way as to include either a
measuring instrument that measures a temperature distribution of an
optical element to which a thermal load is applied, or an energy
detector that detects a laser energy as a detector that detects the
beam parameters equivalent to the direction of the laser beam and
the shape of the wave front thereof, whereby the direction of the
laser beam and the shape of the wave front thereof are predicted
based on a signal from the measuring instrument or a signal from
the energy detector.
[0027] Further, a window of the chamber, or a window of the
amplifier, or a window of the saturable absorption cell may be
configured as a diamond window.
[0028] It is possible to detect only the direction of laser beam
and control the direction of laser beam to a predetermined
direction according to the result of the detection. Further, a
mirror which reflects laser beam can be provided with a cooling
mechanism for cooling a mirror surface in an axial symmetrical
fashion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a configurational diagram of an EUV light source
device according to a first embodiment of the present
invention;
[0030] FIG. 2 is an explanatory diagram of a saturable
absorber;
[0031] FIG. 3 is a graph showing changes in the temperature of the
saturable absorber;
[0032] FIG. 4 is a configurational diagram of a wave front
compensator;
[0033] FIG. 5 is an exemplary diagram of a sensor;
[0034] FIG. 6 is another exemplary diagram of the sensor;
[0035] FIG. 7 is a flowchart of a wave front compensating
process;
[0036] FIG. 8 is a flowchart of a process in which a laser
controller notifies an EUV light source controller of completion of
adjustment;
[0037] FIG. 9 is a configurational diagram of an EUV light source
device according to a second embodiment;
[0038] FIG. 10 is a flowchart of a wave front compensating
process;
[0039] FIG. 11 is a configurational diagram of an EUV light source
device according to a third embodiment;
[0040] FIG. 12 is a configurational diagram of an EUV chamber;
[0041] FIG. 13 is a configurational diagram of an isolator;
[0042] FIG. 14 is a flowchart of a wave front compensating
process;
[0043] FIG. 15 is a configurational diagram of an EUV light source
device according to a fourth embodiment;
[0044] FIGS. 16A to 16C are explanatory diagrams showing how to
arrange a wave front compensator according to a fifth
embodiment;
[0045] FIGS. 17A and 17B are explanatory diagrams which are a
continuation of FIGS. 16A to 16C;
[0046] FIGS. 18A to 18D are configurational diagrams of a wave
front curvature compensator according to a sixth embodiment;
[0047] FIGS. 19A and 19B are a configurational diagram of a wave
front curvature compensator according to a seventh embodiment;
[0048] FIG. 20 is a configurational diagram of a wave front
curvature compensator according to an eighth embodiment;
[0049] FIG. 21 is a configurational diagram of a wave front
curvature compensator according to a ninth embodiment;
[0050] FIG. 22 is a configurational diagram which is a continuation
of FIG. 21;
[0051] FIG. 23 is a configurational diagram of a wave front
curvature compensator according to a tenth embodiment;
[0052] FIG. 24 is a configurational diagram which is a continuation
of FIG. 23;
[0053] FIGS. 25A to 25C are configurational diagrams of a wave
front curvature compensator according to an eleventh
embodiment;
[0054] FIGS. 26A to 26C are configurational diagrams which are a
continuation of FIGS. 25A to 25C;
[0055] FIG. 27 is a general configurational diagram of an EUV light
source device;
[0056] FIGS. 28A to 28C are configurational diagrams of a wave
front curvature compensator according to a twelfth embodiment;
[0057] FIG. 29 is a configurational diagram of an angle compensator
according to a thirteenth embodiment;
[0058] FIGS. 30A and 30B are configurational diagrams of a wave
front compensator according to a fourteenth embodiment;
[0059] FIGS. 31A and 31B are configurational diagrams of a wave
front compensator according to a fifteenth embodiment;
[0060] FIGS. 32A and 32B are configurational diagrams of a wave
front compensator according to a sixteenth embodiment;
[0061] FIG. 33 is a configurational diagram of a wave front
compensator according to a seventeenth embodiment;
[0062] FIG. 34 is a configurational diagram of a wave front
compensator according to an eighteenth embodiment;
[0063] FIG. 35 is a configurational diagram of a sensor according
to a nineteenth embodiment;
[0064] FIG. 36 is a configurational diagram of a sensor according
to a twentieth embodiment;
[0065] FIG. 37 is a configurational diagram of a sensor according
to a twenty-first embodiment;
[0066] FIG. 38 is a configurational diagram of a sensor according
to a twenty-second embodiment;
[0067] FIG. 39 is a configurational diagram of a sensor according
to a twenty-third embodiment;
[0068] FIG. 40 is a block diagram of a wave front compensation
controller according to a twenty-fourth embodiment;
[0069] FIG. 41 is an explanatory diagram showing the essential
portions of a chamber to a twenty-fifth embodiment;
[0070] FIG. 42 is a configurational diagram of an optical sensor
unit according to a twenty-sixth embodiment;
[0071] FIG. 43 is a configurational diagram of an optical sensor
unit according to a twenty-seventh embodiment;
[0072] FIGS. 44A to 44C are explanatory diagrams showing
interference fringes;
[0073] FIG. 45 is a configurational diagram of an optical sensor
unit according to a twenty-eighth embodiment;
[0074] FIG. 46 is a configurational diagram of an optical sensor
unit according to a twenty-ninth embodiment;
[0075] FIG. 47 is a configurational diagram of a light receiving
element;
[0076] FIGS. 48A to 48C are explanatory diagrams showing the
relationship between the beam shape of laser beam and the output of
the light receiving element;
[0077] FIGS. 49A and 49B are explanatory diagrams of an optical
sensor unit according to a thirtieth embodiment;
[0078] FIGS. 50A and 50B are explanatory diagrams which are a
continuation of FIGS. 49A and 49B;
[0079] FIGS. 51A and 51B are explanatory diagrams which are a
continuation of FIGS. 50A and 50B;
[0080] FIG. 52 is a configurational diagram of an isolator
according to a thirty-first embodiment;
[0081] FIG. 53 is an explanatory diagram showing an example of a
preferable combination of the embodiments;
[0082] FIG. 54 is a configurational diagram of an EUV light source
device according to a thirty-second embodiment;
[0083] FIG. 55 is a configurational diagram of an EUV light source
device according to a thirty-third embodiment;
[0084] FIG. 56 is a configurational diagram of a vapor deposition
device according to a thirty-fourth embodiment;
[0085] FIG. 57 is an explanatory diagram showing the relationship
between a mirror and a wave front curvature compensator according
to a thirty-fifth embodiment;
[0086] FIG. 58 is a rear view of the mirror;
[0087] FIG. 59 is a cross-sectional view of the mirror;
[0088] FIG. 60 is a rear view of a mirror according to a
thirty-sixth embodiment;
[0089] FIG. 61 is a cross-sectional view of the mirror;
[0090] FIG. 62 is a cross-sectional view of a mirror according to a
thirty-seventh embodiment; and
[0091] FIG. 63 is a cross-sectional view of a mirror according to a
thirty-eighth embodiment.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0092] Preferred embodiments of the present invention will be
described below with reference to the accompanying drawings.
According to the embodiments, at least one compensation means (34,
44) for compensating the wave front of laser beam is provided on an
optical path where laser beam passes. The compensation means can
arrange the traveling direction of laser beam and the shape of the
wave front thereof. While a laser light source device to be used in
an extreme ultraviolet light source device will be described
herein, the invention can be adapted to other laser light source
devices than the laser light source device for use in an extreme
ultraviolet light source device.
First Embodiment
[0093] A first embodiment of the invention will be described
referring to FIGS. 1 to 8. FIG. 1 is an explanatory diagram showing
the general configuration of an EUV light source device 1. The
characteristic configurations of the invention as seen in the
individual embodiments to be described below are not limited to the
illustrated combinations, but it is noted that various other
combinations are possible and are included within the scope of the
invention.
[0094] The EUV light source device 1 is configured to have, for
example, a chamber 10 for generating EUV radiation, a laser light
source device 2 for supplying laser beam to the chamber 10, and an
EUV light source controller 70. The laser light source device 2
includes, for example, a laser oscillator (master oscillator) 20
which determines the time-dependent waveform of a laser pulse and
the repeating frequency, an amplification system 30, a focusing
system 40, a wave front compensation controller 50, and a laser
controller 60. The EUV light source device 1 supplies EUV radiation
to an EUV exposure device 5.
[0095] First, the outline of the chamber 10 will be described. The
chamber 10 has, for example, a chamber body 11, a connecting unit
12, a window 13, an EUV collector mirror 14, and a target material
supply unit 15.
[0096] The chamber body 11 is kept in a vacuum state by an
unillustrated vacuum pump. The chamber body 11 can be provided
with, for example, a mechanism or the like for collecting
debris.
[0097] The connecting unit 12 is provided to connect between the
chamber 10 and the EUV exposure device 5. EUV radiation generated
in the chamber 10 is supplied to the EUV exposure device 5 via the
connecting unit 12.
[0098] The window 13 is provided at the chamber body 11. Driver
laser beam from the laser light source device 2 enters the chamber
10 through the window 13.
[0099] The EUV collector mirror 14 is a mirror for reflecting EUV
radiation to be collected at an intermediate focus IF. The
intermediate focus IF is set in the connecting unit 12. The EUV
collector mirror 14 is configured as, for example, a concave
surface like a rotary ellipsoid which idealistically does not
generate aberration to transfer an image at a plasma emission point
to the intermediate focus IF. A multilayer coating which includes,
for example, a molybdenum coating and a silicon coating is provided
at the top surface of the EUV collector mirror 14 to reflect EUV
radiation with a wavelength of 13 nm or so.
[0100] The target material supply unit 15 supplies a target
material, such as tin, in the form of a solid or liquid. Tin may be
supplied as a tin compound such as stannane (SnH4). In case where
tin is supplied in the form of liquid, it can be achieved by a
method of supplying tin in the form of a solution containing tin or
supplying tin in the form of a colloidal solution containing tin or
a tin compound in addition to a method of heating pure tin to the
melting point to be liquefied. Although tin droplets DP will be
explained as a target material by way of example according to the
embodiment, the invention is not limited to tin droplets. For
example, other materials, such as lithium (Li) and xenon (Xe), may
be used as well.
[0101] First, the action in the chamber 10 will be briefly
described. Driver laser beam is focused at a predetermined position
in the chamber body 11 through the input window 13. The target
material supply unit 15 drops the tin droplets DP toward the
predetermined position. At the timing at which the tin droplets DP
reach the predetermined position, the laser light source device 2
outputs driver laser beam L1 of predetermined power. The tin
droplets DP are irradiated with the driver laser beam L1 to become
plasma PLZ. The plasma PLZ radiates EUV radiation L2. The EUV
radiation L2 is collected at the intermediate focus IF in the
connecting unit 12, and is supplied to the EUV exposure device
5.
[0102] Next, the configuration of the laser light source device 2
will be described. The laser light source device 2 is configured as
a carbon dioxide gas pulse laser light source device, and outputs
pulses of driver laser beam L1 with, for example, a wavelength of
10.6 .mu.m, a single lateral mode, a repeating frequency of 100
kHz, 100 to 200 mJ and 10 kW to 20 kW.
[0103] The laser beam output from the laser oscillator 20 is
amplified by the amplification system 30, and is supplied to the
focusing system 40. The focusing system 40 supplies the driver
laser beam L1 into the chamber 10. The focusing system 40 has, for
example, a reflection mirror 41, an off-axis parabolic concave
mirror 42, and a relay optical system 43. The side of the laser
oscillator 20 will be called "upstream side" and the side of the
chamber 10 will be called "downstream side" hereinafter with the
traveling direction of laser beam as a reference.
[0104] The amplification system 30 has, for example, an relay
optical system 31, a preamplifier 32, a saturable absorber 33, a
wave front compensator 34, a chamber 10 main amplifier 35, and a
sensor 36. Hereinafter, the saturable absorber 33 will be called
"SA 33". It is noted that the power of laser beam may be enhanced
by using an MOPA (Master Oscillator and Power Amplifier).
[0105] The relay optical system 31 is an optical system for
adjusting the spread angle of the beam of laser beam output from
the laser oscillator 20, and the size of the beam in order to
efficiently fill the amplification area in the preamplifier 32 with
the laser beam output from the laser oscillator 20. The relay
optical system 31 expands the beam radius of the laser beam output
from the laser oscillator 20 to convert the beam to a predetermined
beam flux.
[0106] The preamplifier 32 amplifies input laser beam, and outputs
the amplified laser beam. The laser beam amplified by the
preamplifier 32 is input to the SA 33. The SA 33 demonstrates a
function of passing laser beam having an intensity equal to or
higher than a predetermined threshold value, and inhibiting passing
of laser beam having an intensity less than the predetermined
threshold value. Accordingly, the SA 33 absorbs laser beam (return
light) returning from the chamber 10 and parasitic oscillating
radiation or self-excited oscillating radiation from the main
amplifier 35 to prevent the preamplifier 32 and the laser
oscillator 20 from being damaged. Further, the SA 33 serves to
suppress a pedestal and enhance the quality of the pulse waveform
of laser beam. The "pedestal" is a minute pulse which is generated
in close proximity time to the main pulse.
[0107] FIG. 2 shows an example of the configuration of the SA 33.
The SA 33 has, for example, a holder 330 with an unillustrated
water cooling jacket, two windows 332 and 333 mounted to the holder
330, a flow inlet 334 through which a sulfur hexafluoride gas (SF6
gas) flows in, and a flow outlet 335 from which the SF6 gas flows
out.
[0108] The laser beam L1 amplified by the preamplifier 32 enters
through the left input window 332, and passes through the right
output window 333. The SF6 gas supplied to a clearance between the
windows 332 and 333 serves to absorb the carbon dioxide gas.
[0109] FIG. 3 is a graph showing a temperature distribution
occurring in the SA 33. The SF6 gas enters the clearance between
the windows 332 and 333 from the flow inlet 334, absorbs laser beam
with an intensity equal to or lower than the threshold value, and
flows out from the flow outlet 335. Accordingly, a temperature
distribution which shifts in the flow direction of the SF6 gas
occurs in the SA 33. The temperature distribution of the windows of
the SA 33 changes the distribution of the refractive indexes of the
windows.
[0110] As a result, the laser beam L1 passing the SA 33 is shifted
in a direction AX1e shifted from a reference optical axis AX1 as
shown by a broken like L1e in FIG. 2. The wave front of the laser
beam L1 passing through the SA 33 does not change concentrically
while maintaining the reference optical axis AX1, but is curved
along the axis AX1e. That is, as the laser beam L1 passes through
the SA 33, the direction of the laser beam is shifted, and the
shape of the wave front of the laser beam is changed.
[0111] Even if laser beam Lie whose traveling direction and wave
front shape are changed is input to the main amplifier 35 directly,
an amplification action cannot be obtained as expected. This is
because the amplification area in the main amplifier 35 cannot be
efficiently filled with the laser beam.
[0112] To overcome the problem, the wave front compensator 34 as
the "first compensation unit" is provided between the SA 33 and the
main amplifier 35. The wave front compensator is expressed by "WFC"
(Wave Front Compensator) occasionally in the following description
and the drawings.
[0113] FIG. 4 is an explanatory diagram exemplarily showing the
principle of the wave front compensator 34. The upper side of FIG.
4 shows a case where a low thermal load is applied to the
amplification system 30. The lower side of FIG. 4 shows a case
where a high thermal load is applied to the amplification system
30.
[0114] The wave front compensator 34 has an angle compensator 100
and a wave front curvature compensator 200. The angle compensator
100 is an optical system for adjusting the angle (traveling
direction) of laser beam. The wave front curvature compensator 200
is an optical system for adjusting the curvature of the wave front
of laser beam (spreading of the beam). Specific configurational
examples will be described later as different embodiments.
[0115] The angle compensator 100 is configured to include, for
example, two reflection mirrors 101 and 102 disposed in parallel
and opposite to each other. As shown on the lower side of FIG. 4,
the reflection mirror 101, 102 is provided rotatable about an X
axis (vertical axis in FIG. 4) and a Y axis (axis on the same plane
as the X axis and orthogonal thereto) as the rotational center.
That is, each reflection mirror 101, 102 is mounted in such a way
as to be able to tilt and roll.
[0116] In case of a low thermal load, the laser beam L1 travels
along the reference optical axis, so that it is unnecessary to
change the state of each reflection mirror 101, 102. In case of a
high thermal load, the laser beam Lie is input off the reference
optical axis. Accordingly, the state of each reflection mirror 101,
102 is changed adequately to match with the outgoing direction of
the laser beam.
[0117] The wave front curvature compensator 200 includes, for
example, a convex lens 201 and a concave lens 202. A concave wave
and a convex wave can be corrected to a plane wave by adjusting the
relative position of the convex lens 201 and the concave lens
202.
[0118] The wave front compensation controller 50 as the
"compensation control unit" adequately drives the angle compensator
100 and the wave front curvature compensator 200 so as to cancel a
deviation from a target value based on the result of measurement
performed by the sensor 36. Accordingly, the wave front compensator
34 corrects the angle of the input laser beam and the curvature of
the shape of the wave front thereof to a predetermined direction
and predetermined wave front shape before outputting the laser
beam. The wave front compensator 34 expands the beam radius of the
laser beam in such a way as to provide a beam angle and wave front
curvature which are needed for efficient amplification by the main
amplifier 35, thereby converting the laser beam to a predetermined
laser beam flux. The converted laser beam is amplified by the main
amplifier 35.
[0119] The sensor 36 as the "first detection unit" is provided
downstream of the main amplifier 35 to detect the angle of the
input laser beam and the curvature of the wave front thereof. The
sensor 36 should be configured to be able to directly or indirectly
measure the angle of laser beam and the curvature of the wave front
thereof.
[0120] The outline of the sensor 36 will be described referring to
FIGS. 5 and 6. Other configurational examples of the sensor 36 will
be described later as different embodiments. As shown in the
principle diagram of FIG. 5, the sensor 36 is configured to
include, for example, a reflection mirror 300 which reflects laser
beam L1, and an optical sensor unit 360 which measures laser beam
L1L slightly transmitting through the reflection mirror 300.
[0121] FIG. 6 shows an example of the sensor 36. The reflection
mirror 300 coated with a coating which reflects the laser beam at a
high reflectivity has a beam splitter board 300A and a holder 300B
with an unillustrated water cooling jacket for holding the beam
splitter board 300A.
[0122] The beam splitter board 300A is formed of a material, such
as silicon (Si), zinc selenide (ZnSe), gallium arsenide (GaAs) or
diamond. While most of the laser beam L1 is reflected by the
high-reflectivity coating, very slight laser beam L1L transmits
through the beam splitter board 300A.
[0123] The laser beam L1L transmitted through the beam splitter
board 300A very slightly is input to the optical sensor unit 360.
As the optical sensor unit 360, for example, a beam profiler for
measuring the intensity distribution of laser beam, a power sensor
(calorie meter, pyroelectric sensor or the like) for measuring the
laser duty and the load of an optical element, a wave front sensor
capable of simultaneously measuring the state of the wave front of
laser beam and the direction of the wave front thereof, or the like
can be used.
[0124] Further, as will be described later, the state of the wave
front of laser beam and the angle (direction) of the wave front
thereof may be predicted using parameters (temperature, operational
instruction value, etc.) relating to the state of laser beam and a
data base obtained through simulation, empirical results or the
like.
[0125] Next, the control system will be described. As shown in FIG.
2, the EUV light source device 1 has the wave front compensation
controller 50, the laser controller 60, and the EUV light source
controller 70.
[0126] FIG. 7 is a flowchart illustrating a wave front compensating
process which is executed by the wave front compensation controller
50. This process is executed at the time the laser light source
device 2 is invoked before starting operating. That is, the at the
adjustment stage before the operation of the laser light source
device 2 starts, first, before irradiation on a target, an
unillustrated shutter or the like, for example, is closed to
inhibit laser beam from being input to the EUV chamber 10, and
then, adjusting oscillation of the laser is carried out. Then, when
seed laser beam is output from the laser oscillator 20, the wave
front of laser beam and the angle (direction) thereof are adjusted
in such a way that the amplification efficiency of the main
amplifier 35 is kept high in a laser beam line downstream of the
laser oscillator 20. It is noted that individual flowcharts to be
described herein below illustrate the outlines of the individual
processes which may differ from the actual computer programs. It is
noted that so-called persons skilled in the art would be able to
change or delete illustrated steps, or add new steps. Hereinafter,
the direction of laser beam is occasionally called "angle".
[0127] The wave front compensation controller 50 acquires a
measured value from the sensor 36 (S10), and calculates a
difference .DELTA.D between a target value and the measured value
(S11). The wave front compensation controller 50 determines whether
or not the absolute value of the difference .DELTA.D is equal to or
smaller than a predetermined allowable value DTh (S12). The
allowable value DTh is set to a value which does not affect, for
example, the amplification characteristic of laser beam.
[0128] When the absolute value of the difference .DELTA.D between
the target value and the measured value is equal to or smaller than
the allowable value DTh (S12: YES), the wave front compensation
controller 50 outputs an OK signal to the laser controller 60
(S13). The OK signal is an adjustment complete signal which means
that the wave front of laser beam has been adjusted to a
predetermined wave front (curvature and direction).
[0129] When the absolute value of the difference .DELTA.D is
greater than the allowable value DTh (S12: NO), on the other hand,
the wave front compensation controller 50 outputs an NG signal to
the laser controller 60 (S14). The NG signal is an adjustment
incomplete signal which means that the wave front of laser beam has
not been adjusted to a predetermined wave front.
[0130] The wave front compensation controller 50 outputs a drive
signal to the wave front compensator 34 to cause the wave front
compensator 34 to execute a compensation operation (S15). In
response to the drive signal, the wave front compensator 34
operates the angle compensator 100 and the wave front curvature
compensator 200. As the compensation operation is executed once or
plural times, the wave front of laser beam is matched with the
predetermined wave front.
[0131] FIG. 8 is a flowchart illustrating the operation of the
laser controller 60 and the operation of the EUV light source
controller 70. Upon reception of the OK signal from the wave front
compensation controller 50 (S20: YES), the laser controller 60
notifies the EUV light source controller 70 of completion of the
adjustment of the laser light source device 2 (S21).
[0132] Upon reception of the notification of the adjustment
completion from the laser controller 60, the EUV light source
controller 70 controls the target material supply unit 15 to supply
droplets DP to the chamber body 11 (S22).
[0133] The laser controller 60 controls the laser oscillator 20 to
output the laser beam L1 at the timing of supplying the droplets
DP. The laser beam L1 is amplified by the amplification system 30,
and is then input to the chamber 10 via the focusing system 40. The
droplets DP are irradiated with the laser beam L1 to become plasma
PLZ. EUV radiation L2 radiated from the plasma PLZ is collected at
the intermediate focus IF by the EUV collector mirror 14, and sent
to the EUV exposure device 5.
[0134] According to the embodiment, as described above, the wave
front compensator 34 for adjusting the curvature of the wave front
of laser beam and direction thereof and the sensor 36 for detecting
the curvature of the wave front of laser beam and direction thereof
are provided in the amplification system 30 for amplifying laser
beam output from the laser oscillator 20. According to the
embodiment, therefore, the wave front compensator 34 can adjust the
curvature of the wave front of laser beam and direction (angle)
thereof before the operation of the laser light source device 2
starts. This can stabilize the output characteristic of laser beam
even in an operational state where the thermal load is high.
[0135] According to the embodiment, to adjust the angle (direction)
of laser beam and the curvature of the wave front thereof in the
amplification system 30, the focusing characteristic of laser beam
to be sent to the chamber 10 via the focusing system 40 can also be
maintained stably to some extent.
[0136] According to the embodiment, as mentioned above, laser beam
with stable power can be focused at a predetermined position (the
focal position of the EUV collector mirror and the target) in the
chamber 10. Therefore, the EUV light source device 1 according to
the embodiment can stably generate high-power EUV radiation.
Second Embodiment
[0137] A second embodiment will be described referring to FIGS. 9
and 10. Because individual embodiments to be described below are
modifications of the first embodiment, their descriptions are
mainly about the differences from the first embodiment. According
to the second embodiment, the focusing system 40 is also provided
with a mechanism for performing wave front compensation (wave front
compensator 44, sensor 45 and wave front compensation controller
50(2)).
[0138] FIG. 9 is an explanatory diagram showing the general
configuration of an EUV light source device 1 according to the
embodiment. According to the embodiment, the second wave front
compensator 44 as the "second compensation unit" and the second
sensor 45 as the "second detection unit" are provided in the
focusing system 40.
[0139] Further, the embodiment includes a second wave front
compensation controller 50(2) for compensating laser beam in the
focusing system 40 in addition to a first wave front compensation
controller 50(1) for compensating laser beam in the amplification
system 30.
[0140] FIG. 10 is a flowchart illustrating the operation of the
embodiment. According to the embodiment, as will be described
below, the curvature and the direction (angle) of the wave front of
laser beam are corrected in order from the upstream side. First,
the wave front compensation controller 50(1) which controls the
wave front compensator 34 in the amplification system 30 acquires a
measured value from the sensor 36 (S30), and calculates a
difference .DELTA.D1 (S31).
[0141] The wave front compensation controller 50(1) determines
whether or not the absolute value of the difference .DELTA.D1 is
equal to or smaller than an allowable value DTh1 (S32). When the
absolute value of the difference .DELTA.D1 is equal to or smaller
than the allowable value DTh1 (S32: YES), the wave front
compensation controller 50(1) outputs an OK signal to the laser
controller 60 (S33).
[0142] When the absolute value of the difference .DELTA.D1 is
greater than the allowable value DTh1 (S32: NO), the wave front
compensation controller 50(1) outputs an NG signal to the laser
controller 60 (S34). The wave front compensation controller 50(1)
instructs the wave front compensator 34 to execute a compensation
operation to reduce the difference between the target value and the
measured value (S35).
[0143] Upon reception of the OK signal from the wave front
compensation controller 50(1) (S40: YES), the laser controller 60
notifies the completion of the wave front compensation at the
previous stage to the wave front compensation controller 50(2)
which manages the wave front compensator 44 (S41). This
notification is shown as "OK signal 1" in FIG. 10.
[0144] The wave front compensation controller 50(2) acquires a
measured value from the sensor 45 (S50), and calculates a
difference .DELTA.D2 between the target value and the measured
value (S51). The wave front compensation controller 50(2)
determines whether or not the notification of the completion of the
wave front compensation at the previous stage has been received
from the laser controller 60 (S52).
[0145] The wave front compensation controller 50(2) repeatedly
executes the steps S50 and S51 until the wave front compensation by
the wave front compensation controller 50(1) is completed (S52).
When the wave front compensation by the wave front compensation
controller 50(1) at the previous stage is completed (S52: YES), the
wave front compensation controller 50(2) determines whether or not
the absolute value of the difference .DELTA.D2 calculated in the
step S51 is equal to or smaller than an allowable value DTh2
(S53).
[0146] When the absolute value of the difference .DELTA.D2 is equal
to or smaller than the allowable value DTh2 (S53: YES), the wave
front compensation controller 50(2) outputs the OK signal to the
laser controller 60 (S54). When the absolute value of the
difference .DELTA.D2 is greater than the allowable value DTh2 (S53:
NO), the wave front compensation controller 50(2) outputs a drive
signal to the wave front compensator 44, so that the wave front
compensator 44 executes an operation to compensate the curvature
and the direction (angle) of the wave front of laser beam
(S56).
[0147] Upon reception of the OK signal from the second wave front
compensation controller 50(2) (S42: YES), the laser controller 60
notifies the EUV light source controller 70 of the completion of
the adjustment of the laser light source device 2 (S43).
[0148] According to the embodiment, after completion of the wave
front compensating process on the upstream side (in the
amplification system) is confirmed, the wave front compensating
process on the downstream side (in the focusing system) is carried
out. It is therefore possible to prevent the wave front
compensation by the wave front compensation controller 50(1) and
the wave front compensation by the wave front compensation
controller 50(2) from having contention, which would otherwise
disable execution of sufficient wave front compensation or result
in failure of the wave front compensation.
[0149] The embodiment demonstrates advantages similar to those of
the first embodiment. Further, because wave front compensation of
laser beam is executed even in the focusing system 40 according to
the embodiment, the beam focusing performance can be made more
stable.
Third Embodiment
[0150] A third embodiment will be described referring to FIGS. 11
to 14. According to the embodiment, wave front compensators 34(1),
34(2), 34(3) and 34(4) are associated with amplifiers 32(1), 32(2),
35(1) and 35(2), and wave front compensation of laser beam is
executed every time laser beam is amplified.
[0151] FIG. 11 is a general configurational diagram of an EUV light
source device 1 according to the embodiment. According to the
embodiment, two slab type preamplifiers 32(1), 32(2) are used as
preamplifiers. As laser beam travels along a zigzag optical path in
the slab type preamplifier 32(1), 32(2), the laser beam is
amplified. A plurality of main amplifiers 35(1), 35(2) are provided
in association with the plurality of preamplifiers provided. That
is, pulse beam output from the laser oscillator (MO) 20 is
amplified by the plurality of preamplifiers. Then, the amplified
pulse beam passes through the plurality of main amplifiers to be
amplified further. The individual amplifiers are arranged in series
to amplify the pulse beam.
[0152] A spatial filter 37 for improving the spatial lateral mode
is provided on the output side of the laser oscillator 20. Further,
an SA 33(1) is provided at the output side of the preamplifier
32(1), and an SA 33(2) is provided at the output side of another
preamplifier 32(2).
[0153] The wave front compensator 34(1) and a sensor 36(1) are
provided on the downstream side (laser beam output side) of the
first SA 33(1). The wave front compensator 34(2) and a sensor 36(2)
are provided on the downstream side of the second SA 33(2).
[0154] Laser beam which has passed the sensor 36(2) is reflected by
reflection mirrors 38(1), 38(2) to be input to the wave front
compensator 34(3). The wave front compensator 34(3) is provided on
the upstream side (laser beam input side) of the main amplifier
35(1). A sensor 36(3) corresponding to the wave front compensator
34(3) is provided downstream of the main amplifier 35(1).
[0155] The wave front compensator 34(4) is provided on the upstream
side of the last main amplifier 35(2). A sensor 36(4) is provided
downstream of the main amplifier 35(2).
[0156] A wave front compensator 44 and sensor 45 are also provided
in the focusing system 40 as per the second embodiment. Further,
according to the embodiment, a polarization splitting isolator 46
is provided between a reflection mirror 41(1) and a reflection
mirror 41(2).
[0157] A description will be given of the behavior of laser beam in
the amplification system 30 and the focusing system 40. First, as
laser beam output from the laser oscillator 20 transmits through
the spatial filter 37, the spatial lateral mode is improved. The
laser beam with the improved spatial lateral mode is input to the
input window of the slab type preamplifier 32(1), is amplified
while passing in zigzag manner between two concave mirrors, and is
output from the output window.
[0158] The laser beam amplified by the preamplifier 32(1) passes
through the SA 33(1). As a result, laser beam with an intensity
equal to or lower than a predetermined threshold value is removed
from the laser beam. When the laser beam passes through the SA
33(1), the curvature and the direction (angle) of the wave front of
the laser beam change as described above referring to FIG. 2.
[0159] Accordingly, the laser beam affected by the SA 33(1) is
compensated by the wave front compensator 34(1). A wave front
compensation controller (WFC1-C) 50(1) detects the state of the
laser beam after wave front compensation based on the measured
value from the sensor 36(1), and controls the wave front
compensator 34(1) in such a way that the curvature and angle of the
wave front of laser beam become predetermined values.
[0160] The laser beam compensated by the wave front compensator
34(1) is input to the second preamplifier 32(2) to be amplified
therein, and then passes through the SA 33(2). The wave front of
the laser beam having passed the SA 33(2) is compensated in the
same manner as described above. Based on the measured value from
the sensor 36(3), a wave front compensation controller (WFC2-C)
50(2) outputs a drive signal to the wave front compensator 34(2) in
such a way that the curvature and angle of the wave front of laser
beam become predetermined values.
[0161] The laser beam compensated by the wave front compensator
34(2) is passes through the main amplifier 35(1) and the sensor
36(3) to be input to the wave front compensator 34(3) via the two
reflection mirrors 38(1), 38(2). A wave front compensation
controller (WFC3-C) 50(3) controls the wave front compensator 34(3)
based on the measured value from the sensor 36(3) provided on the
output side of the main amplifier 35(1). The wave front
compensation controller 50(3) operates the wave front compensator
34(3) to acquire the wave front which can efficiently fill the
laser amplification area of the main amplifier 35(1) with laser
beam.
[0162] The laser beam compensated by the wave front compensator
34(3) passes through the main amplifier 35(1) and the sensor 36(3)
to be input to the wave front compensator 34(4). Based on the
measured value from the sensor 36(4) provided on the output side of
the main amplifier 35(2), a wave front compensation controller
(WFC4-C) 50(4) controls the wave front compensator 34(4) in such a
way that the curvature and the direction (angle) of the wave front
of laser beam become predetermined values, as described in the
foregoing description of the wave front compensator 34(3).
[0163] According to the embodiment, laser beam is amplified four
times in total, and the curvature and the angle of the wave front
of the laser beam are compensated in the amplification system 30.
Accordingly, the high-power laser beam output from the last main
amplifier 35(2) is stabilized.
[0164] The laser beam output from the amplification system 30 is
input to the wave front compensator 44 in the focusing system 40. A
wave front compensation controller (WFC5-C) 50(5) causes the wave
front compensator 44 to execute wave front compensation based on
the signal from the sensor 45 provided before the window 13 of a
chamber 10A. This provides laser beam having a predetermined plane
wave.
[0165] The laser beam compensated by the wave front compensator 44
passes through the polarization splitting isolator 46 to enter the
reflection mirror 41(2). The isolator 46 will be described later
referring to FIG. 13. The laser beam reflected by the reflection
mirror 41(2) is input to the window 13 of the chamber 10A via the
sensor 45.
[0166] FIG. 12 is an explanatory diagram showing the chamber 10A
according to the embodiment. The chamber 10A is separated into two
areas 11(1) and 11(2). One area 11(1) is a focusing area to arrange
laser beam input from the laser light source device 2. The other
area 11(2) is an EUV emission area to irradiate laser beam onto
droplets DP to generate EUV radiation.
[0167] The two areas 11(1), 11(2) are separated by a partition. The
focusing area 11(1) and the EUV emission area 11(2) communicate
with each other through a small hole formed in the partition
separating the areas 11(1), 11(2). The pressure in the focusing
area 11(1) can be set slightly higher than the pressure in the EUV
emission area 11(2). This can prevent debris generated in the EUV
emission area 11(2) from entering the focusing area 11(1).
[0168] The laser beam entering the focusing area 11(1) from the
window 13 is reflected by an off-axis parabolic convex mirror 18 to
be input to an off-axis parabolic concave mirror 16(1). As the
laser beam is reflected by the mirror 18 and the mirror 16(1), it
has a predetermined beam radius.
[0169] The laser beam set to the predetermined beam radius is input
to a reflection mirror 17 and reflected thereat to enter another
off-axis parabolic concave mirror 16(2). The laser beam reflected
by the off-axis parabolic concave mirror 16(2) enters the EUV
emission area 11(2) to be irradiated onto droplets DP through a
hole portion 14A of the EUV collector mirror 14.
[0170] It is preferable that the windows through which laser beam
passes, such as the window of each amplifier 32(1), 32(2), 35(1),
35(2), the window of each SA 33(1), SA 33(2), and the window of the
chamber 10A, should be formed of a material having the
characteristic of diamond.
[0171] Diamond passes the wavelength of 10.6 .mu.m of a CO2 laser,
and has a high heat conductivity. Even when a large thermal load is
applied, therefore, a temperature distribution is not likely to
occur, thus making difficult to change the shape and the refractive
index. Therefore, the curvature and angle of the wave front of the
laser beam which passes through a diamond window are not likely to
change.
[0172] Because diamond is generally expensive, however, it may be
difficult to form all the windows of diamond due to the cost. In
consideration of the cost, a diamond window can be used for a
window which is used in an element to which a relatively high
thermal load is applied. In this laser system, except for the SA
33, further downstream the location is, the higher the thermal load
becomes, so that it is better to use a diamond window for both
windows of the main amplifier 35 and the window of the EUV chamber
10A to which a relatively high thermal load is applied. Further,
the SA 33 absorbs the CO2 laser beam, so that its thermal load
becomes higher. It is therefore better to use a diamond window for
the SA 33, regardless of whether it is provided on the upstream
side of the beam or the downstream side.
[0173] FIG. 13 is an explanatory diagram showing the configuration
of the isolator 46. The isolator 46 has, for example, a first
mirror 461 with a heat sink 460, a second mirror 462, and a third
mirror 463. The laser beam reflected by the third mirror 463 is
input to the focusing area 11(1) where a focusing optical system
for focusing laser beam in the chamber 10A is provided, through the
window 13 (see FIG. 12) of the reflection mirror 41(2).
[0174] The first mirror 461 passes P polarized light and reflects
only S polarized light by means of a dielectric multilayer coating
provided on the top surface of the first mirror 461. The P
polarized light is absorbed by the substrate of the first mirror
461, and is cooled by the heat sink 460. The laser beam is input to
the first mirror 461 as the S polarized light.
[0175] The S polarized laser beam reflected by the first mirror 461
is input to the second mirror 462 provided obliquely opposite to
the first mirror 461. A .lamda./4 coating which produces a phase
difference of .pi./2 is formed on the top surface of the second
mirror 462. Therefore, the laser beam is reflected by the second
mirror 462 to be converted to circularly polarized light.
[0176] The circularly polarized laser beam is input to the third
mirror 463. The third mirror 463 is coated with a coating which
reflects the P polarized light and S polarized light with a high
reflectivity. The laser beam reflected by the third mirror 463
passes through the focusing area 11(1) where the focusing optical
system for focusing laser beam is provided, and is collected and
irradiated on the droplets to generate plasma PLZ.
[0177] The laser beam reflected by the plasma PLZ returns as
reverse circularly polarized light along the same optical path as
having traveled at the time of irradiation. The return circularly
polarized light is reflected by the third mirror 463 to be input to
the second mirror 462. The laser beam is reflected by the .lamda./4
coating of the second mirror 462 to be converted to P polarized
light.
[0178] The P polarized laser beam is input to the first mirror 461.
The P polarized laser beam input to the first mirror 461 transmits
through the coating of the first mirror 461 and absorbed by the
substrate of the mirror 461 to be converted to heat. The heat is
discharged by the heat sink 460. Therefore, the laser beam which is
reflected by the plasma PLZ to return can be prevented from
returning to the inlet side of the isolator 46. This can prevent
self-excited oscillation caused by the return beam of the driver
laser beam L1.
[0179] The use of the isolator 46 of the reflection optical system
as shown in FIG. 13 can make the deformation of the wave front,
caused by laser beam passing through the isolator 46, smaller than
the use of the isolator of the transmission optical system.
[0180] FIG. 14 is a flowchart illustrating the outline of the
operation according to the embodiment. As mentioned in the
description of the second embodiment, when a plurality of wave
front compensators are provided, wave front compensation is
executed in order from the upstream wave front compensator.
[0181] First, the wave front compensation controller 50(1) executes
first wave front compensation using the wave front compensator
34(1) located on the most upstream side (S35), and notifies the
laser controller 60 of the completion of wave front compensation
(S32).
[0182] Next, after confirming that notification of the completion
of wave front compensation is output from the wave front
compensation controller 50(1) at the preceding stage (S52), the
wave front compensation controller 50(2) executes second wave front
compensation using the wave front compensator 34(2) (S56). Then,
the wave front compensation controller 50(2) notifies the laser
controller 60 of the completion of wave front compensation
(S54).
[0183] Likewise, after confirming that notification of the
completion of wave front compensation is output from the wave front
compensation controller 50(2) at the preceding stage (S62), the
wave front compensation controller 50(3) executes third wave front
compensation using the wave front compensator 34(3) (S66). Then,
the wave front compensation controller 50(3) notifies the laser
controller 60 of the completion of wave front compensation
(S64).
[0184] Likewise, after confirming that notification of the
completion of wave front compensation is output from the wave front
compensation controller 50(3) at the preceding stage (S72), the
wave front compensation controller 50(4) executes fourth wave front
compensation using the wave front compensator 34(4) (S76). Then,
the wave front compensation controller 50(4) notifies the laser
controller 60 of the completion of wave front compensation
(S74).
[0185] After confirming that notification of the completion of wave
front compensation is output from the wave front compensation
controller 50(4) at the preceding stage (S82), the last wave front
compensation controller 50(5) executes last wave front compensation
using the wave front compensator 44 (S86). Then, the wave front
compensation controller 50(5) notifies the laser controller 60 of
the completion of wave front compensation (S84).
[0186] The laser controller 60 receives the notifications of the
completion of wave front compensation from the wave front
compensation controllers 50(1) to 50(5) in order. Upon reception of
every notification of the completion of wave front compensation,
the laser controller 60 notifies the EUV light source controller 70
of the completion of adjustment of the laser light source device
2.
[0187] The embodiment with the foregoing configuration also has
advantages similar to those of the first and second embodiments.
According to the embodiment, the wave front compensators 34(1) to
34(5) are associated with the amplifiers 32(1), 32(2), 35(1) and
35(2) in the amplification system 30, and laser beam is input to
the individual amplifiers at the proper curvature and angle of the
wave front. Therefore, the embodiment can amplify laser beam more
stably than the first and second embodiments.
Fourth Embodiment
[0188] A fourth embodiment will be described referring to FIG. 15.
The embodiment has a total of four preamplifiers 32(1) to 32(4),
and a total of two main amplifiers 35(1) and 35(2). It is noted
that only one SA 33 is provided in the embodiment as compared with
the third embodiment.
[0189] The amplification system according to the embodiment has a
spatial filter 37, a relay optical system 31(1), a preamplifier
32(1), a relay optical system 31(2), a preamplifier 32(2), an SA
33, a wave front compensator 34(1), a sensor 36(1), a wave front
compensator 34(2), a preamplifier 32(3), a sensor 36(2), a wave
front compensator 34(3), a preamplifier 32(4), a sensor 36(3), a
reflection mirror 38(1), a sensor 36(4), a wave front compensator
34(4), a main amplifier 35(1), a sensor 36(4), a wave front
compensator 34(5), a main amplifier 35(2), and a sensor 36(5) in
order from the upstream side.
[0190] The wave front compensator 34(1) compensates laser beam
which passes through the two preamplifiers 32(1), 32(2), and the SA
33. The sensor 36(1) corresponding to the wave front compensator
34(1) is provided downstream of the wave front compensator 34(1). A
modification of the positional relation among the wave front
compensators 34, the sensors 36, and the elements (SA,
preamplifiers, main amplifiers) where a change in the wave front
occurs will be described later referring to FIGS. 16A to 16C and
17A and 17B.
[0191] The wave front compensator 34(2) compensates laser beam
which passes through the preamplifier 32(3). Likewise, The wave
front compensator 34(3) compensates laser beam which passes through
the preamplifier 32(4). The wave front compensator 34(4)
compensates laser beam which passes through the main amplifier
35(1). The wave front compensator 34(5) compensates laser beam
which passes through the main amplifier 35(2).
[0192] The embodiment with the foregoing configuration, like the
third embodiment, compensates the curvature and the angle of the
wave front of laser beam using the upstream wave front compensators
in order. This embodiment has also advantages similar to those of
the third embodiment.
[0193] Further, according to the embodiment, the laser beam whose
wave front is deformed by the two preamplifiers 32(1), 32(2) and
the SA 33 on the upstream side is compensated by the single wave
front compensator 34(1). Because the upstream side has a lower
thermal load than the downstream side, a single wave front
compensator 34(1) can be allowed to serve as a plurality of
elements (32(1), 32(2), 33) which may change the wave front. This
can reduce the manufacturing cost of the laser light source device
2. Hereinafter, the elements which may change the wave front are
occasionally called "wave front change generating unit".
Fifth Embodiment
[0194] A fifth embodiment will be described referring to FIGS. 16A
to 16C and FIGS. 17A and 17B. A modification of the positional
relation among the wave front compensator 34, the sensor 36, and
the wave front change generating unit (32, 35, 33, etc.) will be
discussed in the description of the embodiment. While wave front
compensators include the wave front compensator 34 in the
amplification system 30 and the wave front compensator 44 in the
focusing system 40, the wave front compensator 34 will be described
below as a representing compensator.
[0195] The wave front change generating units which may cause a
thermal-load originated change in the wave front include the
preamplifier 32, the main amplifier 35, the SA 33, the relay
optical system 31, the reflection mirror, a polarizer, a retarder,
and other various optical elements. For the sake of descriptive
convenience, mainly, the preamplifier 32, the main amplifier 35 and
the SA 33 will be described as the wave front change generating
units by way of example.
[0196] FIG. 16A shows a configuration where the wave front
compensator 34 is disposed upstream of the wave front change
generating unit 32, 35, 33, and the sensor 36 is disposed
downstream of the wave front change generating unit 32, 35, 33.
Laser beam is compensated by the wave front compensator 34, and
then input to the sensor 36. The wave front compensation controller
50 controls the wave front compensator 34 in such a way that the
characteristics (curvature and angle of the wave front) of laser
beam to be measured by the sensor 36 become predetermined
characteristics.
[0197] FIG. 16B shows a configuration where the wave front
compensator 34 and the sensor 36 are disposed downstream of the
wave front change generating unit 32, 35, 33. The wave front
compensator 34 is provided between the wave front change generating
unit 32, 35, 33 and the sensor 36.
[0198] Laser beam is input to the wave front compensator 34 after
passing the relay optical system 31 and the wave front change
generating unit 32, 35, 33. The wave front compensation controller
50 controls the wave front compensator 34 in such a way that the
laser beam characteristic (also called "beam characteristic") which
is detected by the sensor 36 becomes a predetermined
characteristic.
[0199] FIG. 16C shows a configuration where the wave front
compensator 34 and the sensor 36 are disposed upstream of the wave
front change generating unit 32, 35, 33. The sensor 36 is provided
between the wave front compensator 34 and the wave front change
generating unit 32, 35, 33. The wave front compensation controller
50 controls the wave front compensator 34 in such a way that the
laser beam characteristic which is detected by the sensor 36
becomes a predetermined characteristic.
[0200] In FIG. 16C, the wave front compensation controller 50
predicts the deformation of the wave front which may be occurred in
the wave front change generating unit 32, 35, 33, and controls the
wave front compensator 34 in such a way that the laser beam returns
to the normal wave front when passing through the wave front
compensator 34 and the wave front change generating unit 32, 35,
33.
[0201] As shown in FIGS. 17A and 17B, a plurality of wave front
compensators 34 or a plurality of sensors 36 may be provided. As
shown in FIG. 17A, the sensor 36(1) and the sensor 36(2) are
respectively disposed upstream and downstream of the wave front
change generating unit 32, 35, 33. The wave front compensator 34(1)
and the sensor 36(1) are provided upstream of the wave front change
generating unit 32, 35, 33. The wave front compensator 34(2) and
the sensor 36(2) are provided downstream of the wave front change
generating unit 32, 35, 33.
[0202] The laser beam which has passed the sensor 36(1) is input to
the wave front compensator 34(2) after transmitting through the
wave front change generating unit 32, 35, 33, and is further input
to the sensor 36(2) after transmitting through the wave front
compensator 34(2). The wave front compensation controller 50
controls the wave front compensators 34(1), 34(2) in such a way
that the laser beam characteristics measured respectively at the
positions of the sensors 36(1) and 36(2) become predetermined
characteristics at the respective positions.
Sixth Embodiment
[0203] A sixth embodiment will be described referring to FIGS. 18A
to 18D. The description of the embodiment will be given of a case
where the wave front curvature compensator 200 is constituted by a
transmission optical system. As shown in FIGS. 18A to 18D, the wave
front curvature compensator 200 can be constituted by using a
convex lens 201 and a concave lens 202.
[0204] FIG. 18A shows how an input plane wave is output as a plane
wave. If the focal position of the convex lens 201 matches with the
focal position of the concave lens 202 at a common focus cf, laser
beam is converted to a concave wave when it transmits through the
convex lens 201 in the state of a plane wave. The concave-wave
laser beam is converted to a plane wave when it transmits through
the concave lens 202.
[0205] FIG. 18B shows how to convert a convex wave to a plane wave.
The convex lens 201 is shifted upstream (left side in FIG. 18A)
from the position shown in FIG. 18A. A focal position F1 of the
convex lens 201 and a focal position F2 of the concave lens 202 lie
on the optical axis of laser beam, with the focus F1 of the convex
lens 201 positioned upstream of the focus F2 of the concave lens
202.
[0206] When laser beam is changed to a convex wave due to the
influence of heat in the wave front change generating unit 32, 35,
33, the laser beam is input to the convex lens 201 in the state of
diverging beam, and is converted to a concave wave by the convex
lens 201. The laser beam converted to the concave wave is converted
to a plane wave as it transmits through the concave lens 202.
[0207] FIG. 18C shows how to convert a convex wave to a plane wave.
The focal position F1 of the convex lens 201 and the focal position
F2 of the concave lens 202 lie on the same optical axis, with the
focus F2 positioned upstream of the focus F1. When convex-wave
laser beam is input to the convex lens 201, it is converted to a
concave wave. The concave-wave laser beam is converted to a plane
wave as it passes the concave lens 202.
[0208] FIG. 18D shows an example where a wave front curvature
compensator 200A is constituted by using two convex lenses 201,
203. The convex lens 201 can be moved leftward and rightward
(optical axial direction) by a single-axis stage 204.
[0209] When laser beam input as a plane wave (parallel beam) is
output as a plane wave (parallel beam), the position of the convex
lens 201 is set so that the focal position of the convex lens 201
matches with the focal position of the convex lens 203.
[0210] When laser beam becomes convergent beam (concave wave) due
to a thermal load, the convex lens 201 is moved to a downstream
position 201R on the optical axis by the single-axis stage 204.
When laser beam becomes diverging beam (convex wave), on the other
hand, the convex lens 201 is moved to an upstream position 201L on
the optical axis by the single-axis stage 204.
Seventh Embodiment
[0211] A seventh embodiment will be described referring to FIGS.
19A and 19B. The description of the embodiment will be given of a
case where the wave front curvature compensator 200B is configured
as a reflection optical system. The wave front curvature
compensator 200B has two reflection mirrors 205(1) and 205(2), and
two off-axis parabolic concave mirrors 206(1) and 206(2). The
reflection mirror 205(1) and the off-axis parabolic concave mirror
206(2) located on the upper side in FIGS. 19A and 19B are attached
to a plate 207. The plate 207 is movable upward and downward in
FIGS. 19A and 19B. Each mirror 205(1), 206(1) moves upward or
downward together with the plate 207.
[0212] FIG. 19A shows the arrangement in a case where laser beam
input as parallel beam (plane wave) is output as parallel beam
(plane wave). In this case, the focal position of the off-axis
parabolic concave mirror 206(1) and the focal position of the
off-axis parabolic concave mirror 206(2) are matched with each
other to be the common focus cf.
[0213] The laser beam is input to the reflection mirror 205(2) from
the left side (upstream side) in FIGS. 19A and 19B and reflected,
and is input to the other reflection mirror 205(1). The laser beam
reflected by the reflection mirror 205(1) is input to the off-axis
parabolic concave mirror 206(1). The laser beam is reflected at a
reflection angle of 45 degrees by the off-axis parabolic concave
mirror 206(1) to be focused at the common focus cf. The laser beam
spreads from the common focus cf and is input to the off-axis
parabolic concave mirror 206(2) to be reflected at a reflection
angle of 45 degrees.
[0214] FIG. 19B shows the arrangement in a case where laser beam
input as convergent beam (concave wave) is converted to parallel
beam (plane wave) before being output. In this case, the plate 207
is moved downstream to shift the focal position of the off-axis
parabolic concave mirror 206(1) downstream on the optical axis. As
a result, the focal position of the off-axis parabolic concave
mirror 206(1) and the focal position of the off-axis parabolic
concave mirror 206(2) are matched with each other on the optical
axis.
[0215] It is noted that when laser beam is input as diverging beam
(convex wave), the plate 207 is moved upstream in FIGS. 19A and
19B.
[0216] In the wave front curvature compensator 200B configured in
the above manner, the reflection mirror 205(1) and the off-axis
parabolic concave mirror 206(1) are fixed to the plate 207, and
both mirrors 205(1) and 206(1) are simultaneously moved onto the
optical axis (in the upward and downward directions in FIGS. 19A
and 19B). According to the embodiment, therefore, the curvature of
the wave front can be compensated by matching the optical axis of
the input beam with the optical axis of the output beam.
[0217] Further, because the wave front curvature compensator 200B
according to the embodiment is configured as a reflection optical
system, a heat-originated change in the wave front can be made
smaller even when laser beam transmits through the wave front
curvature compensator 200B. This can compensate the curvature of
the wave front even when high-power laser beam is used.
Eighth Embodiment
[0218] An eighth embodiment will be described referring to FIG. 20.
A wave front curvature compensator 200C according to the embodiment
is constituted by a reflection optical system including an off-axis
parabolic concave mirror 206, an off-axis parabolic convex mirror
208, and two reflection mirrors 205(1) and 205(2).
[0219] The off-axis parabolic concave mirror 206 and the reflection
mirror 205(1) are mounted to a plate 207 movable up and down.
Further, the focal position of the off-axis parabolic convex mirror
208 and the focal position of the off-axis parabolic concave mirror
206 are arranged so as to coincide with each other at the common
focus cf.
[0220] Laser beam with a parallel wave front is reflected by the
off-axis parabolic convex mirror 208, and is input to the off-axis
parabolic concave mirror 206 as diverging beam, and is converted to
a plane wave. The laser beam with a parallel wave front is
reflected by each reflection mirror 205(1), 205(2), and output. As
the plate 207 is moved up or down, the wave front of the input
laser beam can be compensated to a plane wave and output, as per
the seventh embodiment.
[0221] The embodiment with the foregoing configuration also has
advantages similar to those of the seventh embodiment. Further,
according to the embodiment, the combination of the off-axis
parabolic concave mirror 206 and the off-axis parabolic convex
mirror 208 can shorten the distance between both off-axis parabolic
mirrors. Therefore, the overall size can be made smaller as
compared with the seventh embodiment.
Ninth Embodiment
[0222] A ninth embodiment will be described referring to FIGS. 21
and 22. In this embodiment, a wave front curvature compensator
200D, 200E is constituted by arranging a single convex mirror 209
and a single concave mirror 210 in a Z pattern.
[0223] FIG. 21 shows the wave front curvature compensator 200D
constituted by arranging the upstream convex mirror 209 and the
downstream concave mirror 210 in a Z pattern. When diverging laser
beam (convex wave) is input to the convex mirror 209, for example,
the convex mirror 209 reflects the laser beam at a small incident
angle .alpha. equal to or lower than 3 degrees or so. The reflected
laser beam is input to the concave mirror 210 at the incident angle
.alpha., and is converted to parallel beam (plane wave) to be
output.
[0224] For example, as the position of the concave mirror 210 is
moved along the reflection optical axis of the convex mirror 209 as
indicated by an arrow in FIG. 21, the wave front of the laser beam
can be converted to a plane wave.
[0225] FIG. 22 shows the wave front curvature compensator 200E
constituted by arranging the upstream concave mirror 210 and the
downstream convex mirror 209 in a Z pattern. When diverging laser
beam (convex wave) is input to the concave mirror 210, for example,
the concave mirror 210 reflects the laser beam at a small incident
angle .alpha. (e.g., equal to or lower than 3 degrees). The
reflected laser beam is input to the convex mirror 209 at the
incident angle .alpha., and is converted to parallel beam (plane
wave). For example, as the position of the convex mirror 209 is
moved along the reflection optical axis of the concave mirror 210,
the wave front of the laser beam can be converted to a plane wave.
According to the embodiment, the convex mirror 209 and the concave
mirror 210 can constitute the wave front curvature compensator,
thus reducing the manufacturing cost. In addition, the reflection
optical system can reduce a change in wave front which occurs when
laser beam passes the wave front curvature compensator.
[0226] According to the embodiment, the optical axis of laser beam
to be output is moved in parallel from the optical axis of laser
beam to be input. Therefore, an optical system which matches the
optical axis of output beam with the optical axis of input beam may
be added to the embodiment.
Tenth Embodiment
[0227] A tenth embodiment will be described referring to FIGS. 23
and 24. The description of the embodiment will be given of a case
where a wave front curvature compensator 200F, 200G is constituted
by a lens and a mirror.
[0228] FIG. 23 shows a case where a concave lens 211L and a concave
mirror 211M constitute the wave front curvature compensator 200F.
When convergent laser beam (concave wave) is input to the concave
lens 211L, for example, the laser beam is converted to diverging
beam (convex wave). The diverging laser beam is input to the
concave mirror 211M to be reflected as parallel beam.
[0229] When the concave mirror 211M is an off-axis parabolic
concave mirror, the incident angle is set to the incident angle of
the off-axis parabolic concave mirror. When the concave mirror 211M
is a spherical mirror, the incident angle is set to a small angle
(equal to or lower than 5 degrees) in order to reduce the wave
front aberration. As the concave lens 211L is moved along the
optical axis, the wave front of the input laser beam can be
compensated.
[0230] FIG. 24 shows a case where a convex lens 212L and a convex
mirror 212M constitute the wave front curvature compensator 200G.
When diverging laser beam (convex wave) is input to the convex lens
212L, the laser beam becomes convergent beam (concave wave) to be
input to the convex mirror 212M. The laser beam is reflected as
parallel beam by the convex mirror 212M.
[0231] When the convex mirror 212M is an off-axis parabolic convex
mirror, the incident angle is set to the incident angle of the
off-axis parabolic convex mirror. When the convex mirror 212M is a
spherical mirror, the incident angle is set to a small angle (equal
to or lower than 5 degrees) in order to reduce the wave front
aberration. As the convex lens 212L is moved along the optical
axis, the curvature of the wave front of the laser beam can be
compensated.
[0232] According to the embodiment with the foregoing
configuration, the optical axis of the input laser beam matches
with the optical axis of the output laser beam, which is
advantageous over the ninth embodiment. Further, according to the
embodiment, the use of a single lens which is a transmission
optical element can make a heat-originated change in wave front as
compared with the sixth embodiment (FIGS. 18A to 18D) which uses
two lenses.
Eleventh Embodiment
[0233] An eleventh embodiment will be described referring to FIGS.
25 to 27. This embodiment uses a variable mirror which can variably
control the curvature of the reflection surface according to a
control signal from the wave front compensation controller 50. Such
a variable mirror is called "VRWM" (Variable Radius Wave front
Mirror) in the embodiment.
[0234] A wave front curvature compensator 200H according to the
embodiment is constituted by a VRWM. FIG. 25A and FIG. 26A show a
case where laser beam input as a plane wave (parallel beam) is
output as a plane wave (parallel beam). In case of converting a
plane wave to a plane wave, the VRWM is controlled so that the top
surface of the VRWM becomes flat.
[0235] FIG. 25B shows a case where laser beam with a convex surface
(diverging beam) is converted to a plane wave (parallel beam). In
this case, the shape of the VRWM is controlled so that the VRWM has
a concave surface.
[0236] FIG. 25C shows a case where laser beam with a concave
surface (convergent beam) is converted to a plane wave (parallel
beam). In this case, the shape of the VRWM is controlled so that
the VRWM has a convex surface.
[0237] FIG. 26B shows a case where a plane wave is converted to a
concave spherical wave. To convert a plane wave to a concave
spherical wave, the top surface of the VRWM is controlled so as to
have a concave troidal shape (in case of the incident angle of 45
degrees or so). Accordingly, laser beam reflected by the VRWM is
focused at the focal distance F. The spherical wave immediately
after being reflected at the troidal VRWM top surface becomes a
concave spherical wave with a curvature radius R. The focal
distance F is equal to the curvature radius R of the spherical
wave.
[0238] FIG. 26C shows a case where a plane wave is converted to a
convex spherical wave. To convert a plane wave to a convex
spherical wave, the top surface of the VRWM is controlled so as to
have a convex troidal shape (in case of the incident angle of 45
degrees or so). The convex wave reflected by the VRWM becomes a
wave front which is emitted from a point light source at the
position of a focal distance -(minus)F. The spherical wave
immediately after being reflected at the troidal VRWM top surface
becomes a spherical wave with a curvature radius -(minus)R. The
focal distance -F is equal to the curvature radius -(minus)R of the
spherical wave.
[0239] Because the wave front curvature compensator 200H can be
constituted by the VRWM alone according to the embodiment with the
foregoing configuration, the number of parts can be reduced to make
the wave front curvature compensator 200H compact, and compensation
can be carried out in single reflection, thus resulting in high
efficiency.
[0240] The wave front curvature compensator 200H according to the
embodiment can output input laser beam with the optical axis
thereof being changed to 45 degrees. As shown in FIG. 27,
therefore, the wave front curvature compensator 200H can be used at
the position where the optical path of the laser beam is changed by
45 degrees. In this case, the reflection mirror 41 can be omitted,
thus making it possible to simplify the configuration and reduce
the manufacturing cost.
Twelfth Embodiment
[0241] A twelfth embodiment will be described referring to FIGS.
28A to 28C. In this embodiment, a wave front curvature compensator
200J is constituted by arranging a VRWM 213 and a reflection mirror
214 in a Z pattern.
[0242] When laser beam input to the VRWM as a plane wave is output
as a plane wave, as shown in FIG. 28A, the VRWM 213 is controlled
so as to become flat. When laser beam input to the VRWM as a convex
wave is converted to a plane wave, as shown in FIG. 28B, the shape
of the VRWM 213 is set to a concave spherical surface. When laser
beam input to the VRWM as a concave wave is converted to a plane
wave, as shown in FIG. 28C, the shape of the VRWM 213 is set to a
convex spherical surface.
[0243] The embodiment with this configuration also has advantages
similar to those of the eleventh embodiment. It is noted that
according to the embodiment, the input optical axis and the output
optical axis of laser beam are shifted in parallel to each other,
and do not coincide with each other. Therefore, an optical system
may be added to the embodiment to return the optical axis to the
original state.
Thirteenth Embodiment
[0244] A thirteenth embodiment will be described referring to FIG.
29. In this embodiment, a single reflection mirror 102 and a single
plane parallel window 103 constitute an angle compensator 100A. The
reflection mirror 102 and the plane parallel window 103 are
rotatable in both clockwise and counterclockwise in FIG. 29.
[0245] As indicated by a solid-line arrow in the diagram, laser
beam input to the reflection mirror 102 is reflected by the
reflection mirror 102 to be input to the window 103, and transmits
through the window 103 to be output. The optical axis indicated by
the solid-line arrow is a reference optical axis.
[0246] When laser beam is input askew to the reflection mirror 102
as indicated by a broken-line arrow, by way of contrast, the tilt
angle of the reflection mirror 102 is adjusted. Accordingly, the
optical axis of the laser beam reflected by the reflection mirror
102 is set in parallel to the reference optical axis.
[0247] The laser beam parallel to the reference optical axis is
input to the plane parallel window 103. The optical axis of the
laser beam transmitting through the plane parallel window 103 can
be matched with the reference optical axis by adjusting the tilt
angle of the plane parallel window 103.
Fourteenth Embodiment
[0248] A fourteenth embodiment will be described referring to FIGS.
30A and 30B. The description of the embodiment will be given of a
wave front compensator 34A which can serve as an angle compensator
and a wave front compensator. The wave front compensator 34A
includes a VRWM 110 and a reflection mirror 111.
[0249] FIG. 30A shows a case where the thermal load is low.
Plane-wave laser beam is input to the reflection mirror 111 at 45
degrees and is reflected by the reflection mirror 111 to be input
to the VRWM 110 at an incident angle of 45 degrees. The VRWM 110 is
controlled so as to have a flat shape. The laser beam is reflected
at the flat mirror surface of the VRWM 110 to be output in the
state of a plane wave.
[0250] The compensation is not limited to the case of converting
plane-wave input radiation to plane-wave output radiation. The
focal distance of the VRWM can be controlled to a constant value so
that the laser beam input as diverging beam (convex wave) is output
as laser beam whose wave front has a desired curvature.
[0251] FIG. 30B shows a case where the angle (direction) of laser
beam and the curvature of the wave front thereof are changed.
[0252] Suppose that the direction of the input laser beam is tilted
downward in FIGS. 30A and 30B due to the influence of the thermal
load, changing the wave front to diverging beam (convex wave). In
this case, the angle of the reflection mirror 111 is controlled in
such a way that the optical axis of laser beam to be reflected by
the reflection mirror 111 matches with the reference optical
axis.
[0253] The laser beam reflected by the reflection mirror 111 is
input to the VRWM 110 at the incident angle of 45 degrees. The
shape of the VRWM 110 is set to a concave wave in such a way that
the laser beam to be reflected by the reflection mirror 110 becomes
a plane wave.
[0254] The description has been given of the case of converting
convex-wave laser beam to a plane wave, which is not restrictive.
Concave-wave laser beam can be converted to a plane wave, or
convex-wave or concave-wave input radiation can be converted to
output radiation whose wave front has a desired curvature.
[0255] In case where the tilt angle lies within the allowable
aberration, for example, the optical axis of the output beam may be
matched with the reference optical axis by controlling the angles
of the horizontal and vertical axes of the VRWM 110 (controlling
the tilt and roll).
Fifteenth Embodiment
[0256] A fifteenth embodiment will be described referring to FIGS.
31A and 31B. In this embodiment, a wave front compensator 34B
serving as an angle compensator and a wave front compensator is
constituted by arranging a reflection mirror 113 and a VRWM 112 in
a Z pattern. The incident angle is a small angle of 3 degrees or
less. That is, the incident angle is set to an angle which does not
cause aberration.
[0257] FIG. 31A shows a case where the thermal load is low.
Plane-wave laser beam is input to the reflection mirror 113 at an
incident angle of 3 degrees or less to be reflected. The reflected
laser beam is input to the VRWM 112 at an incident angle of 3
degrees or less. The shape of the VRWM 110 is controlled so as to
be flat, and reflects laser beam in the state of a plane wave. The
description has been given of the case of a plane wave, which is
not restrictive. Even when a convex wave or a concave wave is
input, for example, it can be output as laser beam whose wave front
has a desired curvature by changing the shape of the VRWM 112.
[0258] FIG. 31B shows a case where the thermal load is high. A
description will now be given of a case where the angle of the
input laser beam is tilted downward in FIG. 31B and the wave front
of the laser beam becomes a convex wave. In this case, the angle of
the reflection mirror 113 is changed to match the optical axis of
laser beam to be reflected by the reflection mirror 113 with the
reference optical axis (optical axis shown in FIG. 31A).
[0259] The laser beam reflected by the reflection mirror 113 is
input to the VRWM 112 at an incident angle of 3 degrees or less.
The shape of the VRWM 112 is changed to a convex wave and the angle
of the VRWM 112 is adjusted in such a way that the laser beam
reflected by the reflection mirror 110 becomes a plane wave. The
compensation is not limited to the case of converting input beam to
a plane wave, and a concave wave or a convex wave can be converted
to a wave front having a desired curvature to be output. The same
is true of the following embodiments.
Sixteenth Embodiment
[0260] A sixteenth embodiment will be described referring to FIGS.
32A and 32B. In this embodiment, a wave front compensator 34C
serving as an angle compensator and a wave front compensator is
constituted by using two convex lenses 114 and 115. The convex lens
115 is provided on a movable stage 117 for adjusting the position
in a direction orthogonal to the optical axis (up and down
direction in FIGS. 32A and 32B). Further, the movable stage 117 is
provided on another movable stage 118 for adjusting the position in
the optical axial direction. Therefore, the convex lens 115 can be
moved in either one of the optical axial direction and the
direction orthogonal to the optical axis. Reference numeral "119"
denotes a point (focal point) where beam having passed the convex
lens 114 is focused.
[0261] FIG. 32A shows a case where the thermal load is low.
Plane-wave laser beam transmits through the convex lens 114 to be
focused at the focal position. The convex lens 115 is disposed in
such a way that its focal position matches with the focal position
of the convex lens 114 on the same optical axis. The beam focused
at the position becomes diverging beam to be input to the convex
lens 115, and is converted to a plane wave input to be output by
the convex lens 115.
[0262] The compensation is not limited to the case of converting
plane-wave input beam to plane-wave output beam. The focal distance
of the VRWM can be controlled to a constant value so that the laser
beam input as diverging beam (convex wave) is output as laser beam
whose wave front has a desired curvature.
[0263] FIG. 32B shows a case where the thermal load is high. The
input direction of the laser beam is tilted obliquely upward and
becomes diverging beam (convex wave) due to the influence of the
thermal load. This diverging beam is focused at a position farther
than the focal position of the convex lens 114. The position of the
convex lens 114 is moved in the optical axial direction (left and
right direction in FIGS. 32A and 32B) in such a way that the
focusing point matches with the focus of the convex lens 115.
Further, the convex lens 115 is moved in the direction orthogonal
to the optical axis (up and down direction in FIGS. 32A and 32B).
This causes the output direction of the laser beam to match with
the reference optical axis. The laser beam which has passed the
convex lens 114 is input to the convex lens 115 to be converted to
a plane wave, which is output along the reference optical axis.
[0264] It is noted that while achievement of the wave front
compensator 34 which executes angle compensation and compensation
of the curvature of the wave front is not limited to the coupling
of the convex lens 114 and the convex lens 115, the wave front
compensator 34 which executes angle compensation and wave front
curvature compensation may be configured by coupling a single
convex lens 114 to a single concave wave.
Seventeenth Embodiment
[0265] A seventeenth embodiment will be described referring to FIG.
33. In this embodiment, a wave front compensator 34D serving as an
angle compensator and a wave front compensator is constituted by
using a deformable mirror 120 and a reflection mirror 121.
[0266] As shown in FIG. 33, the deformable mirror 120 and the
reflection mirror 121 are arranged in a Z pattern. The shape of the
reflection surface of the deformable mirror 120 is controlled
variably according to a control signal. The deformable mirror 120
is disposed before the preamplifier or between the preamplifier and
the main amplifier. Accordingly, laser beam before being turned
into high-power laser beam is input to the deformable mirror
120.
[0267] When laser beam with a deformed wave front is input to the
deformable mirror 120, the shape of the reflection surface of the
deformable mirror 120 is adjusted according to the input wave
front. The deformable mirror 120 compensates the wave front of the
input laser beam to a plane wave before reflecting the laser beam.
The laser beam compensated to a plane wave is reflected by the
reflection mirror 121 to be output.
[0268] The use of the deformable mirror 120 can allow even a wave
front which is not a spherical wave, e.g., an S-shaped wave front,
to be converted to a plane wave or a desired spherical wave. In
addition, the direction of laser beam can be compensated by a small
angle. Further, the direction of laser beam can be adjusted by
performing tilt and roll controls on each of the reflection mirror
121 and the deformable mirror 120. The same is true of an
eighteenth embodiment to be described next.
[0269] According to the embodiment, the deformable mirror 120 is
disposed before (upstream of) the main amplifier, so that the wave
front of laser beam with relatively low power can be compensated.
According to the art described in JP-A-2003-270551 mentioned above,
by way of contrast, high-power laser beam is input to the
deformable mirror, so that the deformable mirror is likely to be
damaged by the heat of laser beam, and thus has lower reliability.
Because the deformable mirror is constituted as a set of multiple
micro-actuators, it is difficult to effectively cool the deformable
mirror. When high-power laser beam is input to the deformable
mirror, therefore, the deformable mirror is likely to be damaged by
heat.
Eighteenth Embodiment
[0270] An eighteenth embodiment will be described referring to FIG.
34. In this embodiment, a deformable mirror 120 is combined with
polarization control to constitute a wave front compensator 34E.
The wave front compensator 34E has the deformable mirror 120, a
beam splitter 122, and a .lamda./4 plate 123. A wave front change
generating unit 32, 35, 33 can be disposed between the beam
splitter 122 and .lamda./4 plate 123.
[0271] For example, a coating to isolate P polarized light and S
polarized light is provided. Laser beam with P polarization
(polarized wave front including the surface of a sheet) is input to
the beam splitter 122. It is assumed that the wave front of the
laser beam is input to the beam splitter 122 in the state of a
plane wave. It is however assumed that the laser beam travels from
the beam splitter 122 and passes through the wave front change
generating unit 32, 35, 33, thus deforming the wave front in the S
shape.
[0272] The laser beam having passed through the wave front change
generating unit 32, 35, 33 transmits through the .lamda./4 plate
123 to become circularly polarized light. The wave front
compensator 34 deformed in the S shape is compensated to a
predetermined wave front by the deformable mirror 120 adjusted to
an appropriate shape.
[0273] The laser beam with compensated wave front transmits through
the .lamda./4 plate 123 again to be converted to S polarized light.
The S polarized laser beam transmits through the wave front change
generating unit 32, 35, 33 to be converted from the predetermined
wave front to a plane wave. The laser beam converted to the plane
wave is input to the beam splitter 122. The S polarized laser beam
is reflected by the beam splitter 122, and output as a plane wave.
The laser beam can be output in a wave front shape other than a
plane wave by adjusting the shape of the top surface of the beam
splitter 122.
Nineteenth Embodiment
[0274] A nineteenth embodiment will be described referring to FIG.
35. In this embodiment, a sensor 36A is constituted by using a
diffraction mirror 301. A grating 301A is formed on the top surface
of the diffraction mirror 301. The diffraction mirror 301 is
provided with a coolant passage 301B through which a coolant
circulates.
[0275] The diffraction mirror 301 reflects input laser beam at an
angle of 45 degrees. This reflected beam is the 0th order light
which has the highest intensity. The negative primary order light
acquired by diffraction has a low intensity. The optical sensor
unit 360 receives the negative primary order light, and measures
the characteristic of the laser beam.
Twentieth Embodiment
[0276] A twentieth embodiment will be described referring to FIG.
36. In this embodiment, a sensor 36B is constituted by using a
window 300W. The window 300W has a window substrate 300AW and a
holder 300BW for holding the window substrate 300AW. The holder
300BW has an unillustrated water cooling jacket.
[0277] The holder 300BW is disposed tilted in the optical axis of
laser beam. Slight laser beam reflected at the top surface of the
window 300W is input to the optical sensor unit 360 as sample
radiation.
[0278] As the window 300W, for example, the window of the amplifier
32, 35, or the window 13 of the EUV chamber 10 can be used. In this
case, it is unnecessary to provide a window only for the purpose of
acquiring sample radiation for measurement, thus reducing the
manufacturing cost. The window substrate 300AW is made of a
material which, like diamond, passes CO2 laser beam and has high
thermal conductivity.
[0279] Laser beam is slightly reflected at both the top surface and
bottom surface of the plane parallel window 300W, and is input to
the optical sensor unit 360 as sample radiation. Therefore, the
plane parallel window 300W is not suitable for measuring the beam
profile. However, it is possible to focus the sample radiation to
the focal position by means of a collector lens to measure the
position of the focused image and measure the direction of laser
beam. In addition, the duty and power of the laser beam line can be
measured adequately.
Twenty-First Embodiment
[0280] A twenty-first embodiment will be described referring to
FIG. 37. In this embodiment, a sensor 36C is constituted by using
beam profilers 304A and 304B. According to the embodiment, beam
transmitted through a reflection mirror 302A is detected by the
beam profiler 304A, and radiation transmitted through a reflection
mirror 302B is detected by the beam profiler 304B. The angle of the
reflection mirror 302A is adjusted according to the measurement
results from the beam profilers.
[0281] A lens 303A is provided between the rear side of the
reflection mirror 302A and the beam profiler 304A. Likewise, a lens
303B is provided between the rear side of the reflection mirror
302B and the beam profiler 304B.
[0282] As plane-wave laser beam transmits through the relay optical
system 31, and transmits through the wave front change generating
unit 32, 35, 33, the direction of laser beam and the curvature of
the wave front thereof are changed. The laser beam with the changed
direction and the changed curvature of the wave front is input to
the wave front compensator 34. The wave front compensator 34
compensates the curvature of the wave front and the direction of
the laser beam, and outputs resultant laser beam.
[0283] The laser beam compensated by the wave front compensator 34
is reflected by the reflection mirror 302A, and is input to the
reflection mirror 302B. Meanwhile, a transfer lens 303A transfers
sample radiation which has slightly transmitted through the
reflection mirror 302A onto the two-dimensional sensor of the beam
profiler 304A. The two-dimensional sensor measures the beam shape
and position of the laser beam.
[0284] The measurement data from the beam profiler 304A is input to
the wave front compensation controller 50. The wave front
compensation controller 50 transmits a control signal to the wave
front compensator 34 to control the wave front compensator 34 so
that the position of the laser beam becomes a reference
position.
[0285] Meanwhile, a transfer lens 303B transfers the radiation
which has slightly transmitted through the reflection mirror 302B
onto the two-dimensional sensor of the beam profiler 304B. The
two-dimensional sensor measures the beam shape and position of the
laser beam.
[0286] The data measured by the beam profiler 304B is input to the
wave front compensation controller 50. The wave front compensation
controller 50 sends a control signal to an actuator 305 for
adjusting the angle of the reflection mirror 302A, and controls the
angle of the reflection mirror 302A so that the position of the
laser beam to be measured by the beam profiler 304B becomes a
reference position. Further, to control the curvature of the wave
front of the laser beam, the wave front compensation controller 50
sends a control signal to the WFC 34 so that the beam shape of the
laser beam has a predetermined value.
[0287] According to the embodiment with this configuration, the
beam profiler 304A, 304B is disposed on that side (rear side of the
reflection mirror) where laser beam transmits through the
reflection mirror 302A, 302B, the sensor 36C can be configured
compact. Further, it is possible to suppress the influence of a
measurement optical system shown in FIG. 37 on the wave front of
the driver laser beam.
Twenty-Second Embodiment
[0288] A twenty-second embodiment will be described referring to
FIG. 38. In this embodiment, changes in the direction of laser beam
and the curvature of the wave front thereof are predicted based on
a temperature change in the optical element through which the laser
beam transmits.
[0289] A measurement optical system 310 is a window or lens, or a
mirror through which laser beam transmits. The measurement optical
system 310 is mounted to a holder 311. The holder 311 is provided
with a passage 311A through which a coolant flows.
[0290] A temperature sensor 312(1), such as a platinum resistance
thermometer sensor or a thermistor, is provided on the coolant
flow-in side. The temperature sensor 312(1) detects the temperature
of the coolant and outputs a detection signal. A temperature sensor
312(2) is likewise provided on the coolant downstream side.
[0291] A coolant temperature calculating unit 313 calculates the
difference between the coolant temperature on the upstream side and
the coolant temperature on the downstream side, and outputs the
difference to a laser beam characteristic determining unit 314. The
temperature difference is proportional to a heat quantity Q used to
cool the measurement optical system 310 if the flow rate of the
coolant is constant.
[0292] The laser beam characteristic determining unit 314 predicts
the direction of laser beam which transmits through the measurement
optical system 310, and the curvature of the wave front using a
table 315 showing the relation between the coolant temperature and
the direction of laser beam and a table 316 showing the relation
between the coolant temperature and the curvature of the wave
front. The prediction result is input to the wave front
compensation controller 50.
[0293] The table 315 is generated by measuring a
temperature-difference originated change in the direction of laser
beam beforehand, for example, empirically or through simulation.
The table 316 is likewise generated by measuring a
temperature-difference originated change in the curvature of the
wave front beforehand, for example, empirically or through
simulation.
[0294] According to the embodiment, a temperature change in the
measurement optical system 310 is detected as a difference in
coolant temperature, a change in the wave front of laser beam
(angle (direction) and curvature of the wave front) can be
predicted easily. The configuration may be modified so that a
temperature change in the measurement optical system 310 is
measured directly by using a radiation thermometer.
Twenty-Third Embodiment
[0295] A twenty-third embodiment will be described referring to
FIG. 39. In this embodiment, the temperature of the measurement
optical system 310 is detected directly by a temperature sensor
312A. The temperature sensor 312A is covered with a light shielding
plate 317 for protection against laser beam.
[0296] Based on the temperature detected by the temperature sensor
312A, a laser beam characteristic determining unit 314A predicts a
change in the direction of laser beam which transmits through the
measurement optical system 310 and a change in the curvature of the
wave front by referring to tables 315A and 316A.
[0297] The relation between the temperature of the measurement
optical system 310 and the direction of laser beam is preset in the
table 315A through, for example, empirically or through simulation.
Likewise, the relation between the temperature of the measurement
optical system 310 and the curvature of the wave front of laser
beam is preset in the table 316A, for example, empirically or
through simulation.
Twenty-Fourth Embodiment
[0298] A twenty-fourth embodiment will be described referring to
FIG. 40. In this embodiment, based on an operational instruction
from the EUV exposure device 5, the influence of the thermal load
which is generated by driver laser beam is predicted, and wave
front compensation is carried out in such a way as to cancel the
predicted influence of the thermal load.
[0299] The EUV exposure device 5 gives the operational instruction
to the EUV light source controller 70. The operational instruction
includes, for example, pulse energy Eeuv of EUV radiation and the
repeating frequency f (or external trigger signal). The EUV light
source controller 70 outputs a control signal to the laser
controller 60 to supply EUV radiation demanded by the EUV exposure
device 5.
[0300] Suppose that, for example, the EUV energy Eeuv and driver
laser energy Eco2 satisfies a proportional relation Eco2=KEeuv. (It
is however preferable that because the relation is actually
non-linear, the relation between Eeuv and Eco2 should be acquired
empirically and stored in a table.) If the assumption is fulfilled,
the thermal load Wlaser of driver laser beam can be expressed by
Wlaser=dutyKEeuvf.
[0301] A wave front compensation controller 50A has a predicting
unit 36F and a wave front control unit 50A1. The predicting unit
36F predicts a change in the wave front of laser beam in place of
the sensor 36. The wave front control unit 50A1 controls the wave
front compensator 34 based on the predicted wave front change.
[0302] The predicting unit 36F includes, for example, an
operational instruction acquiring unit 320 which acquires an
operational instruction, a laser beam characteristic determining
unit 321, a table 322 showing the relation between the operational
state and the direction of laser beam, and a table 323 showing the
relation between the operational state and the curvature of the
wave front of laser beam.
[0303] Based on the operational instruction from the EUV exposure
device 5, the laser beam characteristic determining unit 321
predicts a change in the wave front of laser beam by referring the
tables 322, 323. The wave front control unit 50A1 controls the wave
front compensator 34 in such a way as to cancel the predicted wave
front change.
Twenty-Fifth Embodiment
[0304] A twenty-fifth embodiment will be described referring to
FIG. 41. In this embodiment, the actual image of the focused driver
laser beam in an EUV chamber 10B is measured to control the wave
front compensator 44.
[0305] A sensor 45A is provided at the EUV emission area 11(2) of
the chamber 10B. The sensor 45A includes, for example, a beam
splitter 330, transfer lenses 331 and 332, and an imaging unit 333.
The imaging unit 333 is constituted by, for example, a CCD (Charge
Coupled Device) for infrared.
[0306] The beam splitter 330 reflects a part of driver laser beam,
focused at a predetermined position, toward the transfer lenses
331, 332. The remaining part of the driver laser beam is absorbed
and turned into heat by a dumper 19.
[0307] A wave front compensation controller 50B outputs a
convergence unit to the wave front compensator 44 in such a way
that the shape and position of the laser beam focused in the
chamber 10B become a predetermined shape and a predetermined
position.
[0308] The configuration may be modified so that the wave front of
driver laser beam is compensated by adjusting the position and
posture of each mirror 16(1), 16(2), 17, 18 in the focusing area
11(1), not by the wave front compensator 44.
[0309] According to the embodiment, because the final focusing
result of driver laser beam is measured to control the wave front
of the driver laser beam, the focusing characteristic can be made
stable with high accuracy.
Twenty-Sixth Embodiment
[0310] A twenty-sixth embodiment will be described referring to
FIG. 42. In this embodiment, a Shack-Hartmann sensor is used as an
optical sensor unit 360A. The Shack-Hartmann sensor 360A includes,
for example, a microlens array 361 having multiple microlenses, and
an imaging device 362, such as CCD for infrared.
[0311] A majority of laser beam is reflected by the reflection
mirror 300. Laser beam which slightly transmits through the
reflection mirror 300 is input to the microlens array 361. Images
at the focusing points of the individual microlenses are measured
by the imaging device 362. The wave front of laser beam can be
measured by analyzing the positions of the focusing points of the
individual microlenses.
[0312] According to the embodiment, the deformation and angle
(direction) of the wave front of laser beam can be measured at the
same time. A pin hole array, a Fresnel lens array or the like may
be used instead of the microlens array.
Twenty-Seventh Embodiment
[0313] A twenty-seventh embodiment will be described referring to
FIGS. 43 and 44A to 44C. In this embodiment, the characteristic of
laser beam is measured based on the interference fringes acquired
by a wedge substrate 363. An optical sensor unit 360B includes the
wedge substrate 363 and an infrared sensor 364. The wedge substrate
363 allows carbon dioxide gas laser beam to transmit
therethrough.
[0314] A majority of laser beam is reflected by the reflection
mirror 300. Laser beam which slightly transmits through the
reflection mirror 300 is input to the wedge substrate 363, and is
reflected at both of the front surface and rear surface of the
wedge substrate 363.
[0315] Interference fringes are produced by overlapping the laser
beam reflected at the front surface and rear surface of the wedge
substrate 363 at a predetermined angle. FIG. 44A shows interference
fringes when laser beam input to the wedge substrate 363 is a plane
wave. FIG. 44B shows interference fringes when laser beam input to
the wedge substrate 363 is a convex wave. FIG. 44C shows
interference fringes when laser beam input to the wedge substrate
363 is a concave wave.
[0316] The interference fringes acquired by the wedge substrate 363
are detected by the infrared sensor 364. A change in the wave front
of the laser beam can be detected based on how the interference
fringes are curved. Further, the direction of the laser beam can be
detected based on the flow direction of the interference
fringes.
[0317] According to the embodiment, the deformation and direction
of laser beam can be measured at the same time. It is noted that it
is difficult to expect the high accuracy as provided by the
Shack-Hartmann sensor. A beam profile, beam pointing, energy meter
or the like may be used instead of the infrared sensor 364.
Twenty-Eighth Embodiment
[0318] A twenty-eighth embodiment will be described referring to
FIG. 45. An optical sensor unit 360C in this embodiment measures a
beam profile and beam pointing.
[0319] Laser beam which has transmitted through the reflection
mirror 300 is separated into reflected radiation and transmitted
radiation by a beam splitter 363A. The transmitted radiation is
focused onto a two-dimensional infrared sensor 366(1) by a focusing
lens 365(1) to measure the focusing performance and direction
(pointing state). The reflected beam is transferred onto a
two-dimensional infrared sensor 366(2) to form an image thereon by
a transfer lens 365(2) to measure the beam profile.
Twenty-Ninth Embodiment
[0320] A twenty-ninth embodiment will be described referring to
FIGS. 46, 47 and 48A to 48C. In this embodiment, an optical sensor
unit 360D is constituted by using a cylindrical lens 367 having a
cylindrical convex surface, a cylindrical lens 368 having a
cylindrical convex surface, and a quadrant light receiving element
369. The buses of both cylindrical lenses are arranged orthogonal
to each other. The definition of "bus" will be given later.
[0321] As shown in FIG. 47, a light receiving surface 369A of the
light receiving element 369 is separated into four diamond-shaped
areas DA1 to DA4. The outputs of the upper and lower light
receiving surfaces DA1 and DA3 are compared with the outputs of the
right and left light receiving surfaces DA2 and DA4, arranged
orthogonal to the light receiving surfaces DA1 and DA3, by an
operational amplifier 369B, and the comparison result is
output.
[0322] When convex-wave laser beam transmits through the lenses
367, 368, as shown in FIG. 48A, it becomes laser beam elongated in
the vertical direction, which is input to the light receiving
element 369. The light receiving element 369 outputs a positive
voltage.
[0323] When concave-wave laser beam transmits through the lenses
367, 368, as shown in FIG. 48C, it becomes laser beam elongated in
the horizontal direction, which is input to the light receiving
element 369. The light receiving element 369 outputs a negative
voltage.
[0324] When plane-wave laser beam transmits through the lenses 367,
368, as shown in FIG. 48B, it becomes approximately circular laser
beam, which is input to the light receiving element 369. The output
of the light receiving element 369 becomes 0. A two-dimensional
sensor may be used instead of the light receiving element 369.
Thirtieth Embodiment
[0325] A thirtieth embodiment will be described referring to FIGS.
49A, 49B, 50A, 50B, 51A and 51B. An optical sensor unit 360E in
this embodiment has two cylindrical lenses 368(1) and 368(2) having
the same focal distances disposed on the optical axis of laser beam
with their buses being orthogonal to each other. The "bus" of the
cylindrical lens is a line connecting the vertexes of a convex
surface. Each cylindrical lens 368(1), 368(2) is constituted as a
cylindrical lens having a cylindrical convex surface.
[0326] A light receiving element is disposed at an intermediate
position D between the focal distance, F1, of the cylindrical lens
368(1) and the focal distance, F2, of the cylindrical lens 368(2).
As the light receiving element, the quadrant light receiving
element shown in FIG. 47, a two-dimensional imaging device or the
like can be used. Hereinafter, the position D where the light
receiving element is disposed is called "sensor position D".
[0327] FIG. 49A shows the focused states of laser beam as seen from
the horizontal direction (X) and the vertical direction (Y) when
plane-wave laser beam has transmitted through the two cylindrical
lenses 368(1), 368(2).
[0328] The upper side of FIG. 49A shows the state of laser beam
when the bus of the first cylindrical lens 368(1) is perpendicular
to the horizontal direction (X), and the bus of the second
cylindrical lens 368(2) is in parallel to the horizontal direction
(X). In this case, with regard to the X direction, the first
cylindrical lens 368(1) serves as a convex lens, and the second
cylindrical lens 368(2) serves as a window.
[0329] Therefore, at the focal position F1 of the cylindrical lens
368(1), laser beam is focused in a line parallel to the direction
perpendicularly orthogonal to the X direction, and then spreads as
diverging beam. At the sensor position D indicated by the broken
line, the laser beam spreads in parallel to the X axis to a given
length L1.
[0330] The lower side of FIG. 49A shows the state of laser beam
when the bus of the first cylindrical lens 368(1) is in parallel to
the vertical direction (Y), and the bus of the second cylindrical
lens 368(2) is perpendicular to the vertical direction (Y). In this
case, with regard to the Y direction, the first cylindrical lens
368(1) serves as a window, and the second cylindrical lens 368(2)
serves as a convex lens.
[0331] Therefore, at the focal position F2 of the cylindrical lens
368(2), laser beam is focused in a line parallel to the direction
orthogonal to the Y direction. Because the sensor position D is
located before the focal position F2, laser beam having a given
length L2 parallel to the Y axis is detected.
[0332] FIG. 49B shows a shape IM1 of laser beam on the XY plane,
which is to be measured at the sensor position D. The
cross-sectional shape IM1 of the laser beam on the XY plane is an
approximately rectangular shape having a width L1 in the X
direction and a width L2 in the Y direction. When the sensor
position D is set in the center of each cylindrical lens 368(1),
368(2) with F1=F2 set, the cross-sectional shape IM1 of the laser
beam becomes a square with L1=L2.
[0333] FIGS. 50A and 50B show the focused states of laser beam when
convex-wave laser beam has transmitted through the two cylindrical
lenses 368(1), 368(2). The upper side of FIG. 50A corresponds to
the upper side of FIG. 49A. The lower side of FIG. 50A corresponds
to the lower side of FIG. 49A. Likewise, the upper side and lower
side of FIG. 51A respectively correspond to the upper side and
lower side of FIG. 49A.
[0334] As shown on the upper side of FIG. 50A, the convex-wave
laser beam is focused in a line at a position (right side in FIG.
50A) slightly farther than the focal position F1 of the cylindrical
lens 368(1) in parallel to the direction orthogonal to the X
direction. The laser beam spreads as diverging beam. At the sensor
position D, the laser beam spreads to a given length Lia parallel
to the X axis.
[0335] As shown on the lower side of FIG. 50A, the convex-wave
laser beam is focused in a line at a position farther than the
focal position F2 of the cylindrical lens 368(2) in parallel to the
direction orthogonal to the Y direction. Because the sensor
position D is located before the focusing point, laser beam has a
given length L2a parallel to the Y axis.
[0336] FIG. 50B shows a shape IM2 of convex-wave laser beam on the
XY plane. The shape IM2 of the laser beam is rectangular having a
width L1a in the X direction and a width L2a in the Y direction and
elongated in the Y direction.
[0337] FIGS. 51A and 51B show the focused states of laser beam when
concave-wave laser beam has transmitted through the cylindrical
lenses 368(1), 368(2). As shown on the upper side of FIG. 51A, the
laser beam is focused in a line at a position before the focal
position F1 of the cylindrical lens 368(1) in parallel to the
direction orthogonal to the X direction. The focused laser beam
then spreads as diverging beam. At the sensor position D, the laser
beam has a given length L1b parallel to the X axis.
[0338] As shown on the lower side of FIG. 51A, the laser beam is
focused in a line at a position before the focal position F2 of the
cylindrical lens 368(2) in parallel to the direction orthogonal to
the Y direction. Because the sensor position D is located before
the focusing point, laser beam has a given length L2b parallel to
the Y axis.
[0339] FIG. 51B shows a shape IM3 of concave-wave laser beam on the
XY plane. The shape IM3 of the laser beam is rectangular having a
width Llb in the X direction and a width L2b in the Y direction and
elongated in the Y direction.
Thirty-First Embodiment
[0340] A thirty-first embodiment will be described referring to
FIG. 52. This embodiment illustrates another example (46A) of a
polarization splitting isolator.
[0341] Laser beam is input in the form of P polarized light to a
beam splitter 464 for separating P polarized light and S polarized
light from each other. The beam splitter 464 passes the P polarized
light and reflects the S polarized light. The laser beam which has
transmitted the beam splitter 464 transmits through a .lamda./4
plate 465 to be converted to circularly polarized light.
[0342] The laser beam is focused and irradiated on droplets via the
optical system in the focusing area 11(1) which focuses the laser
beam. A part of the laser beam returns in the form of circularly
polarized light on the same optical path and enters the .lamda./4
plate 465 again. As the laser beam passes through the .lamda./4
plate 465, it is converted to S polarized light. Therefore, the S
polarized laser beam is reflected by the beam splitter 464 and is
absorbed by a dumper 466.
[0343] The invention is not limited to the foregoing individual
embodiments. It is noted that those skilled in the art can made
various additions, modifications and so forth within the scope of
the invention. It is noted that configurations achieved by
combining the foregoing embodiments are included within the scope
of the invention.
[0344] A driver laser system which supplies laser beam to the EUV
exposure device includes a "driver laser beam line" and a "beam
delivery and focusing optical system". The "driver laser beam line"
is the mechanism that compensates the wave front of a beam line
from the driver laser oscillator 20 to the main amplifier 35 at the
last stage. The "beam delivery and focusing optical system" is the
mechanism that delivers driver laser beam to the window of the EUV
chamber, and irradiates the laser beam on a target material, such
as droplets, by means of the focusing optical system.
[0345] Changes in the wave front which occur in the "driver laser
beam line" are classified into a wave front change caused as the
laser beam transmits through the amplifiers 32, 35, and a wave
front change caused when the laser beam transmits through the SA
33. It is noted that the focusing performance of the focusing
optical system is changed as various optical elements, such as the
reflection mirror, isolator and EUV window, are deformed by
heat.
[0346] FIG. 53 shows an example for compensating a wave front
change caused by radiation transmission through the amplifier, a
wave front change caused by radiation transmission through the
saturable absorption cell, and a wave front change caused by beam
transmission through the focusing optical system.
[0347] In a first case, the wave front compensator is constituted
by a reflection mirror and a VRWM with an incident angle of 45
degrees to compensate a wave front change caused by the amplifier
(FIGS. 30A and 30B). Further, two beam profilers are disposed at
different layout positions (FIG. 37). In the first case, to
compensate a wave front change caused by the saturable absorber,
the wave front compensator is constituted by a reflection mirror
and a VRWM with an incident angle of 45 degrees (FIGS. 30A and
30B), and the sensor shown in FIG. 37 is used.
[0348] In the "beam delivery and focusing optical system" in the
first case, the configuration shown in FIGS. 31A and 31B is
employed as the wave front compensator, and the configuration of
the pointing sensor and the beam profiler, which have been
described referring to FIG. 45, is employed as the sensor. The
configuration shown in FIG. 13 is employed as an isolator.
[0349] In the first case, a plurality of wave front compensators
positioned on the line of driver laser beam are constituted by a
reflection optical system, and the focusing optical system takes
the simple configuration of a reflection optical system. Therefore,
a heat-originated wave front change can be made smaller as compared
with the case where the transmission optical system is
employed.
[0350] Further, the use of the simple beam profiler and pointing
sensor as a sensor can ensure sufficient detection of even a
wavelength of 10.6 .mu.m of a CO2 laser or the like.
[0351] A second case will be described. The configurations of a
wave front compensator and a sensor to compensate a wave front
change caused by the amplifier are the same as those of the first
case (FIGS. 30A and 30B, FIG. 37). A deformable mirror is used for
the wave front compensator to compensate a wave front change caused
by the saturable absorber (FIGS. 30A and 30B, FIG. 37). Further, a
wave front sensor shown in FIG. 42 is used as the sensor.
Accordingly, the wave front which is changed to a complicated wave
front shape by the thermal load can be compensated to a fine wave
front by the deformable mirror. In addition, the wave front sensor
can accurately measure the wave front of laser beam.
[0352] In the "beam delivery and focusing optical system" in the
second case, the configuration including an off-axis parabolic
mirror (FIGS. 19A and 19B or FIG. 20) is used. The wave front
sensor shown in FIG. 42 is employed as the sensor. The
configuration shown in FIG. 13 is employed as an isolator.
[0353] In the second case, the deformation of a wave front caused
by the saturable absorber can be compensated with high accuracy.
Further, because the wave front sensor shown in FIG. 42 is employed
as the sensor in the "beam delivery and focusing optical system",
laser beam can be irradiated on a target (droplets) while detecting
the performance of focusing the laser beam on the target, so that
the output energy of EUV radiation can be made more stable.
[0354] A third case will be described. The wave front compensator
is constituted by a reflection mirror and a VRWM with an incident
angle of 45 degrees to compensate a wave front change caused by the
amplifier (FIGS. 30A and 30B). Further, two beam profilers are
disposed at different layout positions (FIG. 37). The configuration
shown in FIGS. 31A and 31B is used for the wave front compensator
to compensate a wave front change caused by the amplifier, and the
configuration shown in FIG. 46 is used for the sensor. The wave
front compensator and sensor of the saturable absorber are the same
as those of the second case.
[0355] In the "beam delivery and focusing optical system" in the
third case, the configuration shown in FIG. 33 or FIG. 34 is
employed as the wave front compensator, and the configuration of
the wave front sensor shown in FIG. 42 is employed as the sensor.
The isolator and the focusing optical system are the same as those
of the first case and the second case.
[0356] In the third case, the deformation of a wave front caused by
the saturable absorber can be compensated with high accuracy.
Further, because a deformable mirror is employed as the wave front
compensator in the "beam delivery and focusing optical system", and
a wave front sensor is employed as the sensor, laser beam can be
irradiated on a target while detecting the performance of focusing
the laser beam on the target. Therefore, the stability of the
output energy of EUV radiation can be improved more than the second
case.
Thirty-Second Embodiment
[0357] A thirty-second embodiment will be described referring to
FIG. 54. In this embodiment, the configuration of a prepulse laser
and the configuration for compensating the optical characteristic
of the prepulse laser are added to the configuration shown in FIG.
1. When droplets DP reach a predetermined position, prepulse laser
beam L4 is irradiated on the droplets DP. As a result, the target
material is expanded. Therefore, the density of the target material
at the predetermined position where the driver laser beam L1 is
irradiated can be lowered to a proper value, thus making it
possible to increase the generation efficiency of EUV
radiation.
[0358] According to the embodiment, therefore, a prepulse laser
oscillator 90 and an off-axis parabolic concave mirror 92 for
feeding the prepulse laser beam into the chamber 10 through a
window 13(2) are provided. For example, the basic wave, second
harmonics, third harmonics or fourth harmonics of a YAG laser can
be used as the prepulse laser beam. Alternatively, the basic wave
or harmonic radiation of a pulse-oscillating titanium sapphire
laser may be used as the prepulse laser beam. According to the
embodiment, for example, though not illustrated, the target
material supply unit which supplies droplets DP supplies the
droplets DP to the position of the prepulse laser focusing point in
a direction perpendicular to the surface of a sheet.
[0359] Because the tin droplets DP have a diameter of 100 .mu.m or
less, it is necessary to control the beam shape and the focusing
position with high accuracy to irradiate the prepulse laser beam on
the target. According to the embodiment, therefore, a mechanism for
automatically compensating the optical performance of the prepulse
laser beam L4 is provided as described in the foregoing
descriptions of the individual embodiments. The "optical
performance" herein means the focused shape or position of
radiation, or pointing thereof.
[0360] A wave front compensation unit 95 as the "third compensation
unit" is provided between the prepulse laser oscillator 90 and the
off-axis parabolic concave mirror 92. A sensor 96 as the "third
detection unit" is provided between the off-axis parabolic concave
mirror 92 and the window 13(2).
[0361] The prepulse laser beam L4 is input to the off-axis
parabolic concave mirror 92 via the wave front compensation unit
95, and is reflected toward the window 13(2). The sensor 96 detects
the optical performance of the prepulse laser beam L4 traveling
toward the chamber 10, and outputs the detection result to a wave
front compensation controller 97. Then, the wave front compensation
controller 97 controls the wave front compensation unit 95 so that
the optical performance of the prepulse laser beam L4 becomes a
predetermined value.
[0362] According to the invention with the above configuration, the
prepulse laser beam L4 is irradiated on the target material before
the driver laser beam L1 is irradiated on the target material, so
that the generation efficiency of EUV radiation L2 can be made
higher than that achieved by the first embodiment. Further, because
the curvature of the wave front of prepulse laser beam and the
direction thereof can be adjusted in the embodiment, the prepulse
laser beam can be irradiated on the target material more
accurately, thus increasing the efficiency.
Thirty-Third Embodiment
[0363] A thirty-third embodiment will be described referring to
FIG. 55. In this embodiment, prepulse laser beam is amplified by a
plurality of amplifiers 98(1) and 98(2) before being supplied into
the chamber 10.
[0364] The prepulse laser beam output from the prepulse laser
oscillator 90 is input to the first amplifier 98(1) via a first
wave front compensation unit 95(1) to be amplified. The amplified
prepulse laser beam passes through a first sensor 96(1) to enter a
reflection mirror 91(1) to be reflected. A first wave front
compensation controller 97(1) operates the wave front compensation
unit 95(1) based on a detection signal from the sensor 96(1)
provided at the output side of the amplifier 98(1). Accordingly,
the shape of the wave front of prepulse laser beam which passes
through the amplifier 98(1) and the direction of the wave front are
adjusted to desired values.
[0365] The prepulse laser beam reflected by the reflection mirror
91(1) is input to another reflection mirror 91(2) via a second wave
front compensation unit 95(2), and is reflected by the reflection
mirror 91(2). The prepulse laser beam reflected by the reflection
mirror 91(2) passes through the second amplifier 98(2) to be
amplified further. A second wave front compensation controller
97(2) operates the wave front compensation unit 95(2) based on a
detection signal from a sensor 96(2) provided at the output side of
the amplifier 98(2). Accordingly, the shape of the wave front of
prepulse laser beam which passes through the amplifier 98(2) and
the direction of the wave front are adjusted to desired values.
[0366] The prepulse laser beam amplified by the amplifier 98(2)
passes through the second sensor 96(2) to be input to a third wave
front compensation unit 95(3). The prepulse laser beam which has
passed through the third wave front compensation unit 95(3) is
input to the off-axis parabolic concave mirror 92 to be reflected.
The reflected prepulse laser beam passes through the window 13(2)
to be irradiated on the target material in the chamber 10. A third
wave front compensation controller 97(3) operates the wave front
compensation unit 95(3) based on a detection signal from a sensor
96(3) provided at the input side of the window 13(2).
[0367] Accordingly, the shape of the wave front of prepulse laser
beam input into the chamber 10 and the direction of the wave front
are adjusted to desired values.
[0368] A prepulse laser controller 99 operates the prepulse laser
oscillator 90 based on an instruction from the laser controller 60.
Further, the prepulse laser controller 99 controls the individual
wave front compensation controllers 97(1) to 97(3) to compensate
the wave front and angle of prepulse laser beam. When wave front
compensation on the prepulse laser beam is completed, the prepulse
laser controller 99 notifies the laser controller 60 of the
completion.
[0369] The embodiment with this configuration also has advantages
similar to those of the thirty-second embodiment. Further, because
prepulse laser beam is amplified multiple times using a plurality
of amplifiers 98(1), 98(2) in the embodiment, prepulse laser beam
with higher power can be acquired.
[0370] When the plurality of amplifiers 98(1), 98(2) are used,
errors occur in the wave front and position or direction of
prepulse laser beam due to the heat-originated deformation or the
like of the optical system. According to the embodiment, however,
the use of a plurality of wave front compensation units 95(1) to
95(3) and a plurality of sensors 96(1) to 96(3) can compensate the
prepulse laser beam at plural locations. According to the
embodiment, therefore, prepulse laser beam with relatively high
power can be irradiated on the target material accurately and
stably, thus improving the reliability and output efficiency.
Thirty-Fourth Embodiment
[0371] A thirty-fourth embodiment will be described referring to
FIG. 56. The description of this embodiment will be given of a case
where the unique laser light source device of the invention is
adapted to a vacuum vapor deposition device 500.
[0372] FIG. 56 is a general configurational diagram of the vacuum
vapor deposition device 500. This vapor deposition device 500 has
the above-described laser light source device 2. A vapor deposition
chamber 510 has a window 511. A target material 520, a substrate
mounting plate 530, and a substrate 540 to be subjected to vapor
deposition are provided in the vapor deposition chamber 510.
[0373] Driver laser beam output from the laser light source device
2 passes through the window 511 to be input to the target material
520, causing ablation 521. A part of the target material which has
caused the ablation is deposited on the top surface of the
substrate 540 placed on the plate 530.
[0374] As apparent from the above, the laser light source device
according to the invention can be adapted to the vacuum vapor
deposition device 500 as well as the extreme ultraviolet light
source device. Further, the laser light source device according to
the invention can also be adapted to, for example, perforating,
glass processing or the like using ablation.
Thirty-Fifth Embodiment
[0375] A thirty-fifth embodiment will be described referring to
FIGS. 57 to 59. In embodiments to be described below including the
thirty-fifth embodiment, a mirror 600 for inputting laser beam to
an optical element (e.g., VRWM 200H) to compensate the curvature of
the wave front is provided with a function of cooling the mirror
surface in axial symmetry. It is noted that other mirrors than the
mirror for inputting laser beam to the VRWM can also be provided
with the cooling function of the embodiment to be discussed
below.
[0376] FIG. 57 is an explanatory diagram showing the relationship
between the VRWM 200H and a cooling-function equipped mirror
(hereinafter referred to as "mirror") 600. The mirror 600 reflects
input laser beam L1(1). The reflected laser beam L1(2) is input to
the VRWM 200H to be reflected as laser beam L1(3).
[0377] Heat from the laser beam L1(1) is transmitted to the mirror
600. Therefore, thermal expansion or the like would cause irregular
deformation on a mirror surface 602 if no measure were taken
against the heat. If the mirror surface 602 is deformed
irregularly, the wave front of the laser beam L1(2) reflected at
the mirror surface 602 becomes an irregular shape. The irregular
shape is a shape which is neither a concave wave nor a convex wave,
i.e., a shape which is not axially symmetrical to the optical
axis.
[0378] If the shape of the wave front of the laser beam L1(2)
reflected by the mirror 600 becomes axially asymmetrical to the
optical axis, the VRWM 200H cannot shape the wave front of the
laser beam L1(2) to a plane wave. This is because the VRWM 200H,
unlike the deformable mirror capable of coping with various wave
front shapes, can cope only with a concave wave or convex wave
which is symmetrical to the optical axis.
[0379] In this respect, the mirror 600 is provided with the
function of cooling the mirror surface 602 in the axially
symmetrical fashion, so that even when the mirror surface 602 is
deformed by the heat, it is deformed in an axially symmetrical
shape. Accordingly, when the plane-wave laser beam L1(1) is input
to the mirror 600, the wave front of the laser beam L1(2) reflected
by the mirror 600 becomes a convex shape, for example. The VRWM
200H reflects the convex-wave laser beam L1(2) to have a plane
wave.
[0380] Referring to the rear view of the mirror in FIG. 58, the
cooling structure of the mirror 600 will be described. A mirror
body 601 of a metal material having a high thermal conductivity is
formed into a disk shape. The reflection or mirror surface 602 for
reflecting laser beam is formed on one side of the mirror body
601.
[0381] A spiral cooling passage 604 which stretches outward from
the center is formed in the mirror body 601. One end of the cooling
passage 604 communicates with a flow inlet 605 open in a rear side
603 of the mirror 600 at the center portion. The other end of the
cooling passage 604 communicates with a flow outlet 606 open in the
outer periphery of the rear side 603.
[0382] FIG. 59 is a cross-sectional view of the mirror 600. A
cooling pump 610 is connected to the flow inlet 605. A cooler 611
is connected to the flow outlet 606. A coolant like water which is
cooled by the cooler 611 is discharged toward the flow inlet 605
from the cooling pump 610. The coolant which has flowed to the
center portion of the mirror 600 cools the mirror surface 602 while
flowing outward from the center. As a result, the center portion of
the mirror surface 602 is cooled the most. The coolant flows
spirally to cool the mirror surface 602 in such a way that the
temperature of the mirror surface 602 shows an axially symmetrical
distribution. While water is used as the coolant by way of example,
a substance other than water may be used as well. Subsidiary
structures, such as a cooling tank and filter, are not shown.
[0383] According to the embodiment with this configuration, the
mirror 600 which input laser beam to the element 200H for
compensating the wave front is provided with the cooling function
to cool the mirror surface 602 in such a way that the temperature
distribution of the mirror surface 602 becomes axially symmetrical.
Even when the mirror surface 602 is deformed by heat, therefore,
the mirror surface 602 can be deformed axially symmetrically, so
that the wave front of laser beam can be compensated by the VRWM
200H.
Thirty-Sixth Embodiment
[0384] A thirty-sixth embodiment will be described referring to
FIGS. 60 and 61. FIG. 60 is a rear view of a mirror 600A according
to this embodiment. A plurality of annular cooling passages 604(1)
to 604(5) are concentrically provided in the mirror body 601.
[0385] FIG. 61 is a cross-sectional view of the mirror 600A. Each
of the annular cooling passages 604(1) to 604(5) is provided with a
flow inlet and a flow outlet apart from each other in the
diametrical direction. The individual flow inlets are connected to
the discharge port of the cooling pump 610 via a common flow-in
passage 607. The individual flow outlets are connected to the flow
inlet of the cooler 611 via a common flow-out passage 608.
[0386] The temperature of the surface 602 of the mirror 600A is
detected by a temperature sensor 613 configured like a radiation
thermometer. A temperature controller 612 controls the discharge
rate of the cooling pump 610 and the coolant temperature based on
the mirror surface temperature detected by the temperature sensor
613.
[0387] It is noted that, for example, a restriction part may be
provided in a midway of a pipe for supplying the coolant to each of
the annular cooling passages 604(1) to 604(5), and the flow area of
the restriction part is variably controlled by the temperature
controller 612. If the flow area of the restriction part provided
in the cooling passage 604(1) in the center portion of the mirror
600A is increased, for example, the mirror's center portion can be
cooled intensely. The embodiment with this configuration also has
advantages similar to those of the thirty-fifth embodiment.
Thirty-Seventh Embodiment
[0388] A thirty-seventh embodiment will be described referring to
FIG. 62. In the embodiment, each of the annular cooling passages
604(1) to 604(5) in the thirty-sixth embodiment is provided with
the pump 610 and the cooler 611. FIG. 62 shows reference numerals
affixed to some of the pumps and the coolers for the sake of
convenience.
[0389] A temperature controller 612B individually controls the flow
rates and temperatures of the coolants flowing in the cooling
passages 604(1) to 604(5) based on a signal from the temperature
sensor 613. The embodiment with this configuration also has
advantages similar to those of the thirty-fifth embodiment.
Further, because the flow rates and temperatures of the coolants to
be supplied to the cooling passages 604(1) to 604(5) provided
concentrically can be individually controlled according to the
embodiment, the temperature of the mirror surface 602 can be cooled
more property.
Thirty-Eighth Embodiment
[0390] A thirty-eighth embodiment will be described referring to
FIG. 63. FIG. 63 is a cross-sectional view of a cooling-function
equipped mirror according to the embodiment. A plurality of cooling
elements 620, for example, are disposed in the mirror body 601.
Further, temperature sensors 621 for detecting the temperature of
the mirror surface 602 are provided in the mirror body 601. The
cooling element 620 is configured as, for example, an element which
utilizes the Peltier effect. Of both ends of the cooling element
620, the end portion on the side of the mirror surface 602 absorbs
heat, while the end portion on the side of the rear side 603
discharges heat.
[0391] A temperature controller 612C individually controls the
operations of the cooling elements 620 based on detection signals
from the temperature sensors 621. The embodiment with this
configuration also has advantages similar to those of the
thirty-seventh embodiment.
* * * * *